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A non-radioactive assay system for screening for inhibitors of RNA-dependent reverse transcriptase activity; an analysis using aurintricarboxylic acid and plant flavonoids.

Ongoing and extensive screening for potentially selective and potent inhibitors of RNA-dependent DNA polymerases (reverse transcriptases) is important for the discovery of therapeutic agents active against retroviruses. Traditional systems for assaying the activity of reverse transcriptase enzymes have relied upon the use of radioactive nucleotides for monitoring complementary DNA (cDNA) synthesis. Moreover, such assays have also typically been programmed by the addition of synthetic template-primers. The recent trend, however, is towards the use of more natural nucleic acid template-primer-directed systems, which provides for a more realistic estimation of the activity of potential therapeutic anti-reverse transcriptase agents. A novel agarose gel-electrophoretic method originally developed to evaluate DNA polymerase activity during enzyme purification was adapted for screening purposes. The system was modified so that one can detect the synthesis of non-radioactively labeled cDNA synthesized in both DNA and RNA template-directed reverse transcription reactions. Such assays are programmed with either M13mp9 single-stranded DNA or rabbit globin mRNA as appropriate templates. Following incubation of reaction mixtures, agarose gels are used to determine the activity of the DNA-dependent DNA polymerase and RNA-dependent DNA polymerase activities of Maloney murine leukemia virus. This is done through a detection of the amount of double-stranded nucleic acid molecules (either DNA:DNA or RNA:DNA hybrids) generated by the enzyme in the presence and absence of various known enzyme inhibitors. The assay systems that have been developed will be useful in initial, general, rapid, inexpensive and safer screening programs for potential inhibitors of both the DNA- and RNA-dependent DNA-polymerase functions of reverse transcriptase enzymes. The system was tested and evaluated with potent inhibitors of reverse transcription, such as aurintricarboxylic acid and with several plant flavonoids known to be moderately potent inhibitors of reverse transcriptases. The details concerning the RNA-dependent DNA polymerizing system and some of our results are presented.

Animals↗
PubMed1993

Expression and mutational analysis of the reverse transcriptase of the lentivirus equine infectious anemia virus.

The reverse transcriptase of equine infectious anemia virus (EIAV) shows sequence similarity with the reverse transcriptases of other lentiviruses, particularly with those of human immunodeficiency viruses types 1 and 2 (HIV-1 and HIV-2). We have constructed a plasmid that when introduced into E. coli induces the synthesis of substantial quantities of the nearly authentic EIAV reverse transcriptase. The viral and bacterially expressed reverse transcriptases are similar in their molecular weights. The bacterial expression clone was used to generate deletion mutants of the protein. Mutations in both amino and carboxyl terminal regions of the polypeptide strongly affect the DNA polymerase activity of the enzyme. Thus, EIAV reverse transcriptase resembles the reverse transcriptases of HIV-1 and HIV-2 and can serve as a suitable enzyme for studying the structure-function relationship in lentiviral reverse transcriptase.

Cloning, Molecular↗
PubMed1993

Reversal theory: an introduction.

The theory of psychological reversals, or 'reversal theory', is a relatively new theory of motivation and personality that places emphasis on the inconsistency and changeability of human behaviour and experience. The present paper provides a general introduction to the theory's principal constructs and assumptions. Specific reversal theory concepts outlined here include the notions of metamotivational modes, reversals between modes and metamotivational dominance. The nature of metamotivational reversals and factors that influence the process of reversals are also described. Psychometric and experimental research in support of the theory is reviewed. The final section offers a critical evaluation of reversal theory and discusses its relevance and applicability in the health sciences.

Humans↗
PubMed2004

Differential effects of M1 muscarinic receptor blockade and nicotinic receptor blockade in the dorsomedial striatum on response reversal learning.

The present studies determined whether blockade of M(1)-like muscarinic or nicotinic cholinergic receptors in the dorsomedial striatum affects acquisition or reversal learning of a response discrimination. Testing occurred in a modified cross-maze across two consecutive sessions. In the acquisition phase, a rat learned to turn to the left or to the right. In the reversal learning phase, a rat learned to turn in the opposite direction as required during acquisition. Experiment 1 investigated the effects of the M(1)-like muscarinic receptor antagonist, pirenzepine infused into the dorsomedial striatum on acquisition and reversal learning. Experiment 2 examined the effects of the nicotinic cholinergic antagonist, mecamylamine injected into the dorsomedial striatum on acquisition and reversal learning. Bilateral injections of pirenzepine at 10 microg, but not 1 microg, selectively impaired reversal learning. Analysis of the errors indicated that pirenzepine treatment did not impair the initial shift, but increased reversions back to the original response choice following the initial shift. Bilateral injections of mecamylamine, 6 or 18 microg, did not affect acquisition or reversal learning. The results suggest that activation of M(1) muscarinic cholinergic receptors, but not nicotinic cholinergic receptors, in the dorsomedial striatum is important for facilitating the flexible shifting of response patterns.

Animals↗
PubMed2006

The effect of atypical and classical antipsychotics on sub-chronic PCP-induced cognitive deficits in a reversal-learning paradigm.

Phencyclidine (PCP), an NMDA antagonist, has been shown to mimic some aspects of schizophrenia including positive, negative and cognitive symptoms. Previous studies in this laboratory have shown a selective reversal-learning deficit following acute PCP administration, a deficit that is attenuated by atypical, but not classical, antipsychotic treatment. However, acute PCP has limitations for modelling the chronic psychotic illness and persistent cognitive deficits observed in many schizophrenic patients. Therefore, the aim of this study was to examine the cognitive deficit induced by PCP over a longer term using a previously established operant reversal-learning procedure. Moreover, the efficacy of the atypical antipsychotics clozapine, ziprasidone and olanzapine to reverse the sub-chronic PCP deficit was compared with that of the classical antipsychotics, haloperidol and chlorpromazine. Female hooded-Lister rats were trained to respond for food using an operant reversal-learning paradigm. When animals achieved criterion of 90% correct responding they were treated with PCP (2mg/kg) or vehicle twice daily for 7 days, and 7 days later tested for their cognitive ability. PCP induced a significant impairment in the reversal phase relative to the initial phase of the task. Acute ziprasidone (2.5mg/kg), olanzapine (1.5mg/kg) and clozapine (5mg/kg) produced a significant attenuation of the impairment induced by sub-chronic PCP in the reversal phase. In marked contrast to these effects, acute administration of the classical agents haloperidol (0.05 mg/kg) and chlorpromazine (2mg/kg) failed to significantly reverse the PCP-induced cognitive impairment. These data clearly demonstrate that sub-chronic PCP produces enduring and persistent cognitive deficits, effects that are significantly attenuated by atypical but not classical antipsychotics.

Analysis of Variance↗
PubMed2006

Reverse ELISA for IgG and IgM antibodies to detect Lassa virus infections in Africa.

BACKGROUND: Anti-Lassa antibodies are detected by indirect immunofluorescence assay (IFA) or by enzyme-immunoassay (ELISA). Both methods have problems to detect low amounts of specific antibodies. OBJECTIVES: We report here highly sensitive and specific reverse ELISAs to detect Lassa virus IgG and IgM antibodies. Due to the reverse techniques, serum samples could be applied at dilutions of 1:10 without increasing non-specific background reactions. STUDY DESIGN: For IgM antibody detection microtiter plates were coated with anti-IgM antibodies and for IgG antibody detection with rheumatoid factor (RF) (Sachers M, Emmerich P, Mohr H, Schmitz H. Simple detection of antibodies to different viruses using rheumatoid factor and enzyme-labelled antigen (ELA). J Virol Methods 1985;10:99-110). In both assays a tissue culture antigen was used in combination with a labeled anti-Lassa monoclonal antibody (Hufert FT, Ludke W, Schmitz H. Epitope mapping of the Lassa virus nucleoprotein using monoclonal anti-nucleocapsid antibodies. Arch Virol 1989;106(3-4):201-12). RESULTS: The reverse ELISA turned out to detect virus-specific IgG and IgM antibody in all 20 samples of West African patients collected 2-8 weeks after onset of Lassa fever. Moreover, both IFA and reverse ELISA found IgG antibodies in 53 out of 643 samples of healthy West Africans (sensitivity of 100%). Six of the 643 samples were positive by reverse IgG ELISA only. Thus, the specificity compared to IIF was 99.0%, but it may be even higher, because compared to IFA the IgG ELISA was clearly more sensitive in detecting low antibody titers. CONCLUSIONS: In Ghana 3% seropositives were found by IFA, but 4% by the reverse ELISA. The reverse ELISAs can be performed with high sensitivity and specificity under field conditions in Africa.

Africa↗
PubMed2006

The effect of N-methyl-D-aspartate receptor blockade on acetylcholine efflux in the dorsomedial striatum during response reversal learning.

Separate experiments found that activation of N-methyl-d-aspartate (NMDA) receptors or increased acetylcholine (ACh) efflux in the rat dorsomedial striatum is critical for learning when conditions require a shift in strategies. Increasing evidence indicates that NMDA receptor activity affects cholinergic efflux in the basal ganglia. The present studies determined whether NMDA receptor blockade in the dorsomedial striatum with dl-2-amino-5-phosphonopentanoic acid (AP-5) affects dorsomedial striatal ACh output in a resting condition, as well as during response reversal learning. Experiment 1 investigated the effects of AP-5 (12.5, 25 or 50 muM) infused into the dorsomedial striatum on ACh output in a resting condition. AP-5 infusion at 25 and 50 muM led to a 20% and 40% decrease in dorsomedial striatal ACh output, respectively. AP-5 (12.5 muM) infusion did not change dorsomedial striatal ACh output from basal levels. Experiment 2 determined whether dorsomedial striatal ACh efflux increases during response reversal learning and whether AP-5, at a dose that does not affect basal levels, modifies response reversal learning and ACh efflux. Following acquisition of a response discrimination, rats had microdialysis probes bilaterally inserted into the dorsomedial striatum prior to the reversal learning test. After baseline samples, rats received a response reversal learning test for 30 min. Control rats rapidly improved in the reversal learning session while simultaneously exhibiting an approximately 40% increase in ACh output compared with baseline levels. AP-5 (12.5 muM) treatment during testing significantly impaired response reversal learning while concomitantly blocking an increase in ACh output. These findings suggest that NMDA receptor activation in the dorsomedial striatum may facilitate a shift in response patterns, in part, by increasing ACh efflux.

2-Amino-5-phosphonovalerate↗
PubMed1999

Discrimination, reversal, and shift learning in Huntington's disease: mechanisms of impaired response selection.

In a series of three experiments, we investigated different aspects of response selection in early-stage clinically symptomatic Huntington's disease (HD) patients in the context of discrimination learning. A series of structurally related response selection tasks involving discrimination, reversal, and shift learning were employed. In Experiment 1, the mechanisms of our previously reported [37] finding of impaired extra-dimensional shift learning were explored. The results suggested that impaired shift learning in HD is a result of perseverative responding. In Experiment 2, performance on a concurrent-pair (CP) discrimination and reversal task was examined. HD patients showed no deficits in CP discrimination learning or reversal. In Experiment 3, the performance of HD patients on a probabilistic discrimination and reversal task was examined. HD patients were impaired in the learning of a probabilistic discrimination, and also its reversal. This reversal deficit was again the result of perseverative responding. In addition, there was a strong correlation between HD patients' activities of daily living scores and reversal errors. The result are consistent with current theories of the role of the basal ganglia in cognition, and suggest specific impairments in response selection mechanisms in HD, in particular, in overcoming selection biases based on prior reinforcement.

Adult↗
PubMed2002

Attenuation of context-specific inhibition on reversal learning of a stimulus-response task in rats with neurotoxic hippocampal damage.

Rats with hippocampal or sham lesions were trained on a stimulus-response task developed for the 8-arm radial maze. After reaching a stringent learning criterion, different context manipulations were performed. In Experiment I, the different groups were transferred to an identical radial maze in a different room to determine the context specificity of the discrimination learning. Experiment I revealed that although rats with hippocampal lesions did not show a normal context detection effect, the expression of the discrimination was not context dependent for either the lesion or sham groups. In Experiment II, animals were trained to criterion on the discrimination task and then both groups were divided into sub-groups based on whether they would experience reversal training in the same or different context from original training. Experiment II indicated that animals with hippocampal lesions and shams reversed in a different context were significantly enhanced in reaching the learning criterion compared to either counterparts that were reversed in the same context. Reversal learning in rats with hippocampal lesions was faster than sham animals in the same context suggesting that the context-specific inhibition effect was hippocampal-based. After learning the reversal task, the groups of animals trained and reversed in different contexts were brought back into the original training context to test for competitive effects. Animals with hippocampal lesions that were reversed in the different context, did not show a competition between the most recently acquired discrimination and a context-specific association acquired during original training whereas sham animals in the same condition did. Taken together these results suggest that rats with hippocampal lesions do not acquire normal context-specific inhibition during discrimination learning.

Animals↗
PubMed2006

NMDA receptor antagonism impairs reversal learning in developing rats.

Four experiments examined the effect of dizocilpine maleate (MK-801), a noncompetitive N-methyl-Daspartate (NMDA) receptor antagonist, on reversal learning during development. On postnatal days (PND) 21, 26, or 30, rats were trained on spatial discrimination and reversal in a T-maze. When MK-801 was administered (intraperitoneally) before both acquisition and reversal, 0.18 mg/kg generally impaired performance, whereas doses of 0.06 mg/kg and 0.10 mg/kg, but not 0.03 mg/kg, selectively impaired reversal learning (Experiments 1 and 3). The selective effect on reversal was not a result of sensitization to the second dose of MK-801 (Experiment 2) and was observed when the drug was administered only during reversal in an experiment addressing state-dependent learning (Experiment 4). Spatial reversal learning is more sensitive to NMDA-receptor antagonism than is acquisition. No age differences in sensitivity to MK-801 were found between PND 21 and 30.

Animals↗
PubMed1992

Structure of HIV-1 reverse transcriptase/DNA complex at 7 A resolution showing active site locations.

AIDS, caused by human immunodeficiency virus (HIV), is one of the world's most serious health problems, with current protocols being inadequate for either prevention or successful long-term treatment. In retroviruses such as HIV, the enzyme reverse transcriptase copies the single-stranded RNA genome into double-stranded DNA that is then integrated into the chromosomes of infected cells. Reverse transcriptase is the target of the most widely used treatments for AIDS, 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxyinosine (ddI), but resistant strains of HIV-1 arise in patients after a relatively short time. There are several nonnucleoside inhibitors of HIV-1 reverse transcriptase, but resistance to such agents also develops rapidly. We report here the structure at 7 A resolution of a ternary complex of the HIV-1 reverse transcriptase heterodimer, a monoclonal antibody Fab fragment, and a duplex DNA template-primer. The double-stranded DNA binds in a groove on the surface of the enzyme. The electron density near one end of the DNA matches well with the known structure of the HIV-1 reverse transcriptase RNase H domain. At the opposite end of the DNA, a mercurated derivative of UTP has been localized by difference Fourier methods, allowing tentative identification of the polymerase nucleoside triphosphate binding site. We also determined the structure of the reverse transcriptase/Fab complex in the absence of template-primer to compare the bound and free forms of the enzyme. The presence of DNA correlates with movement of protein electron density in the vicinity of the putative template-primer binding groove. These results have important implications for developing improved inhibitors of reverse transcriptase for the treatment of AIDS.

Base Sequence↗
PubMed2001

Effects of selective thalamic and prelimbic cortex lesions on two types of visual discrimination and reversal learning.

The effects of excitotoxic lesions of the mediodorsal nucleus of the thalamus, the anterior thalamic nuclei and of the prelimbic cortex were examined on two tests of discrimination and reversal learning. In experiment 1A (visual discrimination and reversal), rats were required to discriminate two stimuli, and respond to the stimulus associated with reward (the S+ stimulus). There was no effect of lesion on acquisition of this task. However, when stimulus-reward contingencies were reversed, animals with lesions of the mediodorsal nucleus of the thalamus made significantly more errors than control animals or animals of other lesion groups. In experiment 1B (conditional discrimination), animals were required to learn a rule of the type 'If stimulus A then go left, if stimulus B then go right'. No main effect of lesion on acquisition was observed in this experiment. To test the generality of the reversal effect obtained in experiment 1A, a second cohort of animals with the same lesions was tested on acquisition of the visuospatial conditional task immediately postsurgery, followed by the reversal of the conditional rule (experiment 2). As in experiment 1B, no main effect of lesion group was observed during acquisition of the task. However, lesions of the mediodorsal nucleus of the thalamus resulted in a mild impairment according to number of sessions required to attain criterion performance of the task when the response rule was reversed. The results of the present study provide evidence for a role for the mediodorsal nucleus of the thalamus in new learning, particularly when stimulus-reward contingencies are reversed. Furthermore, they show that the functions of this thalamic nucleus can be dissociated from those of the anterior thalamus and the prelimbic cortex.

Animals↗
PubMed2000

Alleviation of overtraining reversal effect by transient inactivation of the dorsal striatum.

In this study, we investigated the role of the dorsal striatum in the acquisition and the use (retrieval) of a specific learning developed during overtraining. The paradigm was such that rats had to respond differentially to two signals in order to obtain food or to avoid an electrical footshock. Overtraining was aimed at eliciting a facilitative effect on discrimination reversal as compared to simply trained rats. In this way, transient inactivation of the dorsal striatum by lidocaine enabled us to investigate, separately, the role of this structure during overtraining and reversal. The data show that inactivating the dorsal striatum before each reversal session prevented the overtraining reversal effect observed in control rats. Moreover, inactivation of the dorsal striatum during overtraining had no effect on the level of discriminative performance just as it did not affect the subsequent facilitative effect on reversal. These results show that even though the striatum might normally be part of a routine automatic system, clearly its contribution is not essential. Indeed, despite inactivation of the striatum in overtrained rats, their ability to develop an efficient selection process that can be used during reversal was observed. However, the integrity of the striatum became essential in order to mediate the modification of behaviour when this behavioural routine formed during overtraining had to be modified during reversal.

Anesthetics, Local↗
PubMed1994

HIV-1 reverse transcription in cord blood lymphocytes: implications for infection of newborns.

We previously demonstrated that progeny virions are not produced after infection of adult quiescent peripheral blood lymphocytes (PBLs) by human immunodeficiency virus type 1 (HIV-1). Molecular analysis revealed that the nonproductive nature of this infection is due to failure to complete reverse transcription of the viral genome. In this study, we examined HIV-1 reverse transcription in quiescent lymphocytes from umbilical cord blood (CBLs). Using the polymerase chain reaction (PCR) to detect the presence of reverse transcription intermediates, we found that as in PBLs from adults, reverse transcription is not completed in quiescent CBLs; instead, a partial reverse transcript is formed. Quantitative PCR analysis also showed that fewer partial reverse transcripts were found in CBLs than in PBLs. Although the relevance of this restriction in reverse transcription to vertical transmission is unclear, these data suggest that the rapid progression of disease in infected children is not due to increased permissiveness of the lymphocytes of newborns for HIV-1 infection.

Adult↗
PubMed2003

Structure-function relationships of the initiation complex of HIV-1 reverse transcription: the case of mutant viruses using tRNA(His) as primer.

Reverse transcription of HIV-1 RNA is initiated from the 3' end of a tRNA3Lys molecule annealed to the primer binding site (PBS). An additional interaction between the anticodon loop of tRNA3Lys and a viral A-rich loop is required for efficient initiation of reverse transcription of the HIV-1 MAL isolate. In the HIV-1 HXB2 isolate, simultaneous mutations of the PBS and the A-rich loop (mutant His-AC), but not of the PBS alone (mutant His) allows the virus to stably utilize tRNA(His) as primer. However, mutant His-AC selects additional mutations during cell culture, generating successively His-AC-GAC and His-AC-AT-GAC. Here, we wanted to establish direct relationships between the evolution of these mutants in cell culture, their efficiency in initiating reverse transcription and the structure of the primer/template complexes in vitro. The initiation of reverse transcription of His and His-AC RNAs was dramatically reduced. However, His-AC-GAC RNA, which incorporated three adaptative point mutations, was reverse transcribed more efficiently than the wild type RNA. Incorporation of two additional mutations decreased the efficiency of the initiation of reverse transcription, which remained at the wild type level. Structural probing showed that even though both His-AC and His-AC-GAC RNAs can potentially interact with the anticodon loop of tRNA(His), only the latter template formed a stable interaction. Thus, our results showed that the selection of adaptative mutations by HIV-1 mutants utilizing tRNA(His) as primer was initially dictated by the efficiency of the initiation of reverse transcription, which relied on the existence of a stable interaction between the mutated A-rich loop and the anticodon loop of tRNA(His).

Base Sequence↗
PubMed1996

Interaction of human immunodeficiency virus type 1 reverse transcriptase with primer tRNALys3 and affinity modification of the enzyme by tRNALys3 derivatives.

The recognition of primer tRNA by retroviral reverse transcriptase is a crucial step in the replication of retroviruses. In the complex formed by HIV-1 reverse transcriptase and its natural primer tRNALys3, the heterodimeric enzyme, p66/p51, binds two molecules of tRNALys3 with different affinities. The same complex but in the presence of a non-complementary template, poly(A), gave higher Kd values. Preincubation of the reverse transcriptase with tRNA at concentrations comparable to the Kd2 value results in different levels of stimulation of the DNA polymerase activity: 300% in the absence and 70-80% in the presence of poly(A). The activation of the catalytically active p66 subunit is most probably mediated through tRNA interaction with the site of reverse transcriptase presenting the lower affinity. In this article, we describe the results obtained with new chemically reactive derivatives of tRNA bearing three or seven hydrophobic residues. Incubation of reverse transcriptase with tRNA derivatives, in the presence or absence of poly(A), leads to covalent binding of the reagents and inactivation of the enzymatic activity. However, during the initial step of the modification reaction, in the absence of poly(A), a slight stimulation of reverse transcriptase by tRNA derivatives took place, followed by a decrease in the enzymatic activity due to the covalent binding of tRNA derivatives to reverse transcriptase. In the presence of poly(A), enzyme inactivation occurs according to pseudo-first-order reaction kinetics. The affinities of tRNA derivatives for the p66/p51 heterodimer estimated from affinity modification data (Kd values) and from the inhibition of polymerization reaction (Ki values) were determined. Each analog of tRNA presented two Kd and two Ki values.

Animals↗
PubMed1978

Reversal of the physiological effects of brief periods of monocular deprivation in the kitten.

1. Five normally reared kittens were monocularly deprived from day 32 to day 42 and then subjected to varying periods (from 6 to 14 days) of deprivation reversal using the technique of reverse suturing. Data obtained from single unit recordings in striate cortex of these kittens were compared to control data from seven normal kittens (aged 32 days to 22.5 weeks) and three normally reared kittens given monocular deprivation from day 32 to day 42. 2. Analysis of cortical ocular dominance patterns in these reverse-sutured kittens revealed a progressively greater shift of influence away from the originally experienced eye and toward the originally deprived eye as the duration of the period of deprivation reversal increased. Most cortical cells were monocularly driven in these animals, but at each stage of the reversal process some binocular neurones were found. 3. The distribution of interocular differences in preferred orientation for binocular cells from these kittens was not significantly different from that for normal kittens, indicating that the pattern of connexions established by the originally deprived eye during reinnervation of striate cortex was very similar to that present before deprivation. 4. Previous studies on reversal of the effects of longer periods of monocular deprivation have indicated that during reinnervation of cortex by fibres representing the originally deprived eye an entirely new and different pattern of connexions is formed. On the basis of these results, it is hypothesized that short-term monocular deprivation causes a reversible silencing of otherwise intact synapses, while terminals are physically disrupted when deprivation is prolonged. 5. This hypothesis is supported by the results of an additional set of experiments in which receptive fields, many of which were highly specific, could be demonstrated for about one-half of the cells studied after removal of the non-deprived eye in two normally reared kittens given 10 days of monocular deprivation beginning on day 32. Similar experiments in two kittens deprived from eye opening to day 42 revealed functional input to less than 20% of the cells studied and no evidence of response specificity.

Afferent Pathways↗
PubMed1995

Human immunodeficiency virus type 1 can use different tRNAs as primers for reverse transcription but selectively maintains a primer binding site complementary to tRNA(3Lys).

The initiation of human immunodeficiency virus type 1 (HIV-1) reverse transcription occurs at a site in the viral RNA genome which is designated the primer-binding site (PBS). The HIV-1 PBS is an 18-nucleotide sequence that is complementary to the 3'-terminal 18 nucleotides of tRNA(3Lys), which is used as the primer for reverse transcription. All HIV-1 isolates sequenced to date contain a PBS complementary to tRNA(3Lys), suggesting that other cellular tRNAs might not function as primers for reverse transcription. To investigate this possibility, we have substituted the HIV-1 PBS with sequences predicted to be complementary to the 3'-terminal nucleotides of tRNA(1,2Lys), tRNA(Ile), and tRNA(His), which previous studies have identified to be packaged into HIV-1 virions along with tRNA(3Lys). We demonstrate that infectious viruses which utilized tRNA(1,2Lys), tRNA(Ile), and tRNA(His) in reverse transcription can be recovered. However, the appearances of viruses with PBSs complementary to these alternate tRNAs were delayed compared with the wild type. After extended in vitro culture, viruses containing the PBSs complementary to these different tRNAs reverted back to the wild-type PBS complementary to tRNA3(Lys). Furthermore, only the first 9 nucleotides of the 18 nucleotide PBSs were sufficient for HIV-1 to utilize the alternate tRNA primers in reverse transcription, demonstrating that HIV-1 does not require the complete 18-nucleotide PBS to utilize these tRNA primers for reverse transcription. These results suggest that factors other than complementarity between the PBS and the primer tRNA contribute to the selectivity of tRNA3(Lys) to initiate HIV-1 reverse transcription.

Acquired Immunodeficiency Syndrome↗