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PubMed1979

Stability of polyadenylic and polyadenylated ribonucleic acids in radish (Raphanus sativus) seedlings.

The stability of polyadenylic acid and polyadenylated RNA was investigated in young radish (Raphanus sativus) seedlings. We first studied the decay of poly(A) content, using a [3H]poly(U) assay, following a complete block of transcription by cordycepin (200 microgram/ml). Two lifetime classes of polyadenylic acid have been determined in these seedlings: a short-lived component with a half-life of 30 min which represents 60% of poly(A) and a more stable component with varying half-lives of which the majority range from 4-10 h and a few are considerably longer. During this period rRNA was shown to decay linearly, taking about 41 h for half of this RNA to disappear. The life-time of the other moiety of polyadenylated-RNA was analysed by continuous labelling with [3H]uridine. We have been able to demonstrate that a significant part of the mRNA molecules turns over with a half-life similar to that of the more slowly turning-over poly(A). No evidence could be obtained for rapidly turning-over messenger RNA. Thus the rapidly turning over poly(A) could correspond to a poly(A) turn-over independent of the remainder of the sequence. When labelling was very long, an apparent steady-state was reached and we determined the polyadenylated RNA content of seedlings to be 2.2% of whole cell RNA. Finally, these results were compared with those previously obtained in studying early germination of radish embryo axes. In contrast with stored mRNA which is rapidly degraded following imbibition, part of the mRNA present in 22 h old seedlings is stable for several hours.

Deoxyadenosines↗
PubMed1984

Interstrand duplexes in Friend erythroleukemia nuclear RNA. The interaction of non-polyadenylated nuclear RNA with polyadenylated nuclear RNA and with small nuclear RNAs.

Intermolecular duplexes among large nuclear RNAs, and between small nuclear RNA and heterogeneous nuclear RNA, were studied after isolation by a procedure that yielded protein-free RNA without the use of phenol or high salt. The bulk of the pulse-labeled RNA had a sedimentation coefficient greater than 45 S. After heating in 50% (v/v) formamide, it sedimented between the 18 S and 28 S regions of the sucrose gradient. Proof of the existence of interstrand duplexes prior to deproteinization was obtained by the introduction of interstrand cross-links using 4'-aminomethyl-4,5',8-trimethylpsoralen and u.v. irradiation. Thermal denaturation did not reduce the sedimentation coefficient of pulse-labeled RNA obtained from nuclei treated with this reagent and u.v. irradiated. Interstrand duplexes were observed among the non-polyadenylated RNA species as well as between polyadenylated and non-polyadenylated RNAs. beta-Globin mRNA but not beta-globin pre-mRNA also contained interstrand duplex regions. In this study, we were able to identify two distinct classes of polyadenylated nuclear RNA, which were differentiated with respect to whether or not they were associated with other RNA molecules. The first class was composed of poly(A)+ molecules that were free of interactions with other RNAs. beta-Globin pre-mRNA belongs to this class. The second class included poly(A)+ molecules that contained interstrand duplexes. beta-Globin mRNA is involved in this kind of interaction. In addition, hybrids between small nuclear RNAs and heterogeneous nuclear RNA were isolated. These hybrids were formed with all the U-rich species, 4.5 S, 4.5 SI and a novel species designated W. Approximately equal numbers of hybrids were formed by species U1a, U1b, U2, U6 and W; however, species U4 and U5 were significantly under-represented. Most of these hybrids were found to be associated stably with non-polyadenylated RNA. These observations demonstrated for the first time that small nuclear RNA-heterogeneous nuclear RNA hybrids can be isolated without crosslinking, and that proteins are not necessary to stabilize the complexes. However, not all molecules of a given small nuclear RNA species are involved in the formation of these hybrids. The distribution of a given small nuclear RNA species between the free and bound state does not reflect the stability of the complex in vitro but rather the abundance of complementary sequences in the heterogeneous nuclear RNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Duplication of functional polyadenylation signals in polyomavirus DNA does not alter efficiency of polyadenylation or transcription termination.

We constructed viable insertion mutants of polyomavirus that contain duplications of the nucleotide sequences surrounding the polyadenylation sites for both E- and L-strand RNAs. Our results showed that formation of poly(A)+ 3'termini of L-strand mRNAs requires sequence elements located between 12 and 87 nucleotides downstream of AAUAAA. No more than 19 nucleotides upstream and 44 nucleotides downstream of AAUAAA are required for polyadenylation of E-strand mRNAs. Our results and those of others suggest that there are three distinct sequence elements required for mRNA 3' end formation: AAUAAA and two downstream elements. An insertion mutant containing two adjacent functional polyadenylation signals produced E-strand and L-strand mRNAs with 3' ends at both sites. However, the overall level of polyadenylation of L-strand RNAs was not increased over the low (10 to 25%) levels seen with wild-type virus. Neither was the efficiency of termination of L-strand transcription increased in mutant virus-infected cells. We conclude that factors required for both polyadenylation and transcription termination are limiting in polyomavirus-infected mouse cells.

Animals↗
PubMed1979

In vitro synthesis of RNA by Xenopus spermatogenic cells I. Evidence for polyadenylated and non-polyadenylated RNA synthesis in different cell populations.

Premeiotic and postmeiotic (haploid) gene expression during spermatogenesis in the anuran, Xenopus laevis, was studied by analyzing the accumulation of radioactively labelled cytoplasmic polyadenylated [poly (A +)] and non-polyadenylated [poly (A -)] RNAs. Dissociated spermatogenic cells were labelled and maintained in an in vitro system capable of supporting cell differentiation. Labelled cells were separated by density gradient centrifugation into subpopulations enriched for individual spermatogenic stages. RNA was extracted and purified from each cell fraction, and separated into poly (A +) and poly (A -) species. Comparison of poly (A +) to non-poly (A) radioactivity in cells labelled with tritiated uridine or adenosine demonstrated that (1) all cell fractions produced significant quantities of polyadenylated RNA relative to total RNA synthesis; and (2) that a cell fraction enriched for pachytene spermatocyte RNA contained up to 15% of total cytoplasmic and 35% of total polysomal RNA labelled as poly (A +) containing species. RNA was also characterized by sucrose density gradient centrifugation and polyacrylamide gel electrophoresis. All cell types showed typical poly (A -) peaks of 4S, 18S and 28S, corresponding to tRNA (4S) and rRNAs (18, 28S) respectively. Spermatids and spermatozoa had additional absorbance peaks at 13 and 21S which cosedimented with Xenopus oocyte mitochondrial rRNA. Patterns of incorporation of uridine and adenosine into poly (A +) RNA in all germ cell fractions tested were complex. In all cases, major areas of radioactivity were found in a broad band sedimenting between 6-17S. Spermatid fractions showed a prominent peak of incorporation at 6-8S, while pachytene cells also showed heavier poly (A +) peaks in the 17-25S region. A non-polyadenylated RNA species sedimenting at 6-8S with a relatively rapid rate of turnover was also observed in spermatids. From these results it is concluded that synthesis of transfer, ribosomal, and putative messenger RNA species continues in spermatogenic cells throughout all but the very last stages of spermatogenesis in Xenopus.

Animals↗
PubMed1980

Relative distribution of post-nuclear poly(A)-containing RNA abundance groups within the nuclear and post-nuclear polyadenylated and non-polyadenylated RNA populations of the lactating guinea-pig mammary gland.

1. RNA isolated from the post-nuclear supernatant of the lactating guinea-pig mammary gland was fractionated with oligo(dT)-cellulose into three populations; those that bound at ;low salt' [long poly(A) tracts, 78-32 nucleotides]; those that bound at ;high salt' [shorter poly(A) tracts, 48-21 nucleotides]; and those that did not bind [no poly(A) or short poly(A) tracts, <20 nucleotides]. Nuclear RNA was fractionated into two populations, those that bound in ;low salt' and those that did not bind. All the post-nuclear RNA fractions directed the synthesis of milk proteins in a Krebs II ascites cell-free system. 2. (3)H-labelled DNA complementary to the post-nuclear poly-(A)-containing RNA population (low-salt fraction) was fractionated into abundant (milk-protein mRNA), moderately abundant and scarce sequences. This complementary DNA was then used to investigate the distribution of the mRNA sequences in the different RNA populations. This showed that all sequences were present in polyadenylated and non-polyadenylated fractions, but that major quantitative differences were apparent. The abundant milk-protein mRNA sequences predominated in the ;low-salt' post-nuclear poly(A)-containing RNA fraction, whereas the moderately abundant sequences predominated in the non-polyadenylated post-nuclear RNA fraction. In total cellular RNA, those sequences deemed initially to be moderately abundant within the ;low-salt' poly(A)-containing RNA population were present at a concentration very similar to those of the abundant milk-protein mRNA (approx. 6x10(5) copies of each sequence/cell). Similarly, analysis of the nuclear RNA populations showed that the ;abundant' and so-called ;moderately abundant' sequences were present in essentially identical concentrations (2x10(3) copies of each sequence/cell). The majority of these (90-95%) were non-polyadenylated. 3. The results are discussed in terms of the post-transcriptional mechanisms involved in the regulation of gene expression in the lactating guinea-pig mammary gland.

Animals↗
PubMed2005

Over-expression of Aurora-A targets cytoplasmic polyadenylation element binding protein and promotes mRNA polyadenylation of Cdk1 and cyclin B1.

Aurora-A is a centrosomal serine-threonine kinase that regulates mitosis. Over-expression of Aurora-A has been found in a wide range of tumors and has been implicated in oncogenic transformation. However, how Aurora-A over-expression contributes to promotion of carcinogenesis remains elusive. Immunohistochemical analysis of breast tumors revealed that over-expressed Aurora-A is not restricted to the centrosomes but is also found in the cytoplasm. This over-expressed Aurora-A appeared to be phosphorylated on Thr288, which is known to be required for its enzymatic activation. In analogy to Aurora-A's role in oocyte maturation and the early embryonic cell cycle, here we investigated whether ectopically over-expressed Aurora-A can similarly stimulate polyadenylation of mRNA in human somatic cultured cells by interacting with a human ortholog of cytoplasmic polyadenylation element binding protein, h-CPEB. In vitro experiments revealed that Aurora-A binds directly to, and phosphorylates, h-CPEB. We found that polyadenylation of mRNA tails of cyclin B1 and Cdk1 was synergistically stimulated when Aurora-A and h-CPEB were over-expressed, and they were further promoted in the presence of an Aurora-A activator Ajuba. Our results suggest a function of ectopically over-expressed Aurora-A that might be relevant for carcinogenesis.

Amino Acid Sequence↗
PubMed1995

XB/U-cadherin mRNA contains cytoplasmic polyadenylation elements and is polyadenylated during oocyte maturation in Xenopus laevis.

Cytoplasmic polyadenylation elements (CPE) are distinct sequence motifs in the 3'-untranslated region of mRNAs. They control translation of these RNAs by cytoplasmic polyadenylation. We show that the mRNA of the cell adhesion molecule XB/U-cadherin contains two CPE motifs. With oocyte maturation this mRNA becomes polyadenylated and increasingly recruited into the polysomal fraction. Our results give evidence that CPEs of the XB/U-cadherin mRNA are responsible for the XB/U-cadherin protein increase during oocyte maturation.

Animals↗
PubMed1992

Developmental profile of polyadenylated and non-polyadenylated GABAA receptor subunit mRNAs.

The ratio of mRNA not selected for polyadenylation (non-poly(A)+ selected) to mRNA selected for polyadenylation (poly(A)+) for the beta 1, alpha 1 and gamma 2 subunits of the GABAA receptor complex was examined in rats as a function of age. RNA was extracted from whole brain of rats that were either 0, 1, 3, 5 or over 60 days of postnatal age. Poly(A)+ mRNA was purified by oligo(dT)-cellulose chromatography. Non-poly(A)+ selected mRNA and poly(A)+ mRNA for the GABAA receptor beta 1, alpha 1 and gamma 2 subunits were examined by Northern blot analysis using cDNA probes specific for these subunits. Levels of GABAA receptor beta 1 subunit mRNA were also examined by solution hybridization analysis with a beta 1 riboprobe. Analysis of Northern blots revealed that levels of poly(A)+ beta 1 subunit mRNA were highest at 0 days of age, but decreased and reached adult levels by 5 days of postnatal age. However, levels of the beta 1 subunit message extracted from non-poly(A)+ selected mRNA were not significantly different at any of the ages examined, suggesting the existence of a population of beta 1 subunit mRNA that is not polyadenylated. The age-related discrepancy between beta 1 subunit levels measured in non-poly(A)+ selected mRNA and poly(A)+ mRNA was also observed using solution hybridization analysis. In contrast, levels of both non-poly(A)+ selected mRNA and poly(A)+ mRNA for the alpha 1 subunit of the GABAA complex increased from 0 days of age to adulthood. Similarly, levels of both non-poly(A)+ selected mRNA and poly(A)+ mRNA for the GABAA receptor gamma 2 subunit increased with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1982

Lectin-induced changes among polyadenylated and non-polyadenylated mRNA in lymphocytes. mRNAs for actin, tubulin and calmodulin respond differently.

The differentiation of T-cell-enriched concanavalin-A-stimulated bovine lymphocytes was studied in vitro. mRNA was isolated from resting and stimulated cells. The amount of polyadenylated RNA increases from 3.6 X 10(-9) to 12 X 10(-9) micrograms/cell during 40 h concanavalin A stimulation. The estimated maximum length of the 3'-poly(A) tract in this RNA is reduced from 240 to 220 residues in stimulated cells. During translation in the rabbit reticulocyte lysate in vitro mRNA from stimulated cells consistently incorporates about 1.6-3 times more radioactivity/micrograms RNA into proteins than mRNA from resting cells. Three translation products have been identified on two-dimensional gels as actin, tubulin and calmodulin. Large quantitative shifts are seen between proteins translated from mRNAs isolated from resting cells and stimulated cells respectively. Actin and calmodulin are already major products from resting cell mRNA. Actin, however, increases about fivefold after stimulation while calmodulin does not change. Tubulin appears in substantial amounts only among stimulated cell mRNA products. Tubulin and calmodulin, on the other hand, remain mainly in the polyadenylated RNA fraction after stimulation while 50% of the actin together with a group of about six other major products is found among proteins translated from non-polyadenylated RNA. We conclude that in lectin-stimulated lymphocytes, besides a general increase in the amount of mRNA, alterations in post-transcriptional processing reactions are active in determining the fate of individual mRNAs.

Actins↗
PubMed1983

Terminal incorporation of 2'-deoxyadenosine into polyadenylate segments of polyadenylated RNA in G1-phase-arrested human T-lymphoblasts.

In the presence of the adenosine deaminase inhibitor erythro-9-[3(2-hydroxynonyl)]adenine microM concentrations of 2'-deoxyadenosine (dAdo) are toxic to nondividing human lymphoid cells and induce G1-phase arrest in T-leukemic lymphoblasts, effects which appear to be independent of ribonucleotide reductase inhibition by accumulated 2'-deoxyadenosine 5'-triphosphate. We sought to determine if 2'-deoxyadenosine 5'-triphosphate had effects similar to those of other cytotoxic adenosine analogues which are incorporated into polyadenylated RNA [poly(A)+ RNA]. In the presence of erythro-9-[3-(2-hydroxynonyl)]adenine, 8-14C]dAdo, at minimal cytostatic concentrations, was incorporated into the polyadenylate segments of cytoplasmic poly(A)+ RNA in the human T-leukemic lymphoblast line CCRF-CEM, and 70% of incorporated dAdo was in the 3'-terminal position. No DAdo was found in enzyme hydrolysates of nonpolyadenylated regions of poly(A)+ RNA or of poly(A)-RNA. Enzymic hydrolysis of polyadenylated segments from labeled poly(A)+ RNA yielded adenosine:dAdo ratios of approximately 55:1.

Adenine↗
PubMedDate not supplied

[Metabolically stable classes of messenger-like nuclear RNA. II. Existence of homology between the 28S fraction of nuclear RNA, giant non-polyadenylated molecules of heterogeneous nuclear RNA and polyadenylated molecules of cytoplasmic RNA].

The existence and extent of homology between the 28S fraction of messenger-like nuclear RNA on one hand, and giant (greater than 45S) molecules of heterogeneous nuclear RNA and various fractions of cytoplasmic RNA on the other hand were studied by the method of competitive hybridization. The results obtained lead to the conclusion that the poly(A)-subfraction of hnRNA molecules with the size of greater than 15 000 nucleotides contains molecules subjected to rapid but incomplete processing with the formation of chains approximately 5000 nucleotides long (approximately 28S), which are then stored in the nucleus for up to 30 hours. Later polyadenylated and non-polyadenylated molecules of cytoplasmic RNA with the size of less than or equal to 2000 nucleotides are formed from the stored precursors.

Animals↗
PubMed1979

Diurnal rhythmicity of nuclear and cytoplasmic polyadenylylated ribonucleic acids and or polyadenylate-dependent polyadenylate polymerase in rat liver.

The hepatic concentration of polyadenylylated RNA was measured in rats kept under LD 12:12. In the nuclei, the concentration was maximal during the dark phase, whereas in the cytoplasm, the highest values were measured during the light phase. The activity of nuclear polyadenylate-dependent polyadenylate polymerase showed a rhythm of low amplitude with a maximum at light-off.

Animals↗
PubMed2001

Recognition of polyadenylation sites in yeast pre-mRNAs by cleavage and polyadenylation factor.

Recognition of poly(A) sites in yeast pre-mRNAs is poorly understood. Employing an in vitro cleavage system with cleavage and polyadenylation factor (CPF) and cleavage factor IA we show that the efficiency and positioning elements are dispensable for poly(A)-site recognition within a short CYC1 substrate in vitro. Instead, U-rich elements immediately upstream and downstream of the poly(A) site mediate cleavage-site recognition within CYC1 and ADH1 pre-mRNAs. These elements act in concert with the poly(A) site to produce multiple recognition sites for the processing machinery, since combinations of mutations within these elements were most effective in cleavage inhibition. Intriguingly, introduction of a U-rich element downstream of the GAL7 poly(A) site strongly enhanced cleavage, underscoring the importance of downstream sequences in general. RNA- binding analyses demonstrate that cleavage depends on the recognition of the poly(A)-site region by CPF. Consistent with in vitro results, mutation of sequences upstream and downstream of the poly(A) site affected 3'-end formation in vivo. A model for yeast pre-mRNA cleavage-site recognition outlines an unanticipated high conservation of yeast and mammalian 3'-end processing mechanisms.

Base Sequence↗
PubMed1994

Expression of polyadenylated and non-polyadenylated trkC transcripts in the rodent central nervous system.

We have previously isolated a full-length cDNA clone encoding rat TrkC, a member of the Trk family of tyrosine kinase receptors, that specifically mediates biological responses to neurotrophin-3. Here, we report the identification of five major trkC transcripts in the adult and developing rat and mouse brain suggesting the presence of several TrkC receptors. Northern blot hybridizations revealed that three of these trkC transcripts (of 14, 3.9 and 4.8 kb) were poly(A)+ messenger RNAs, while the two others, of shorter size (1.1 and 0.7 kb), were poly(A)- messenger RNAs. All transcripts were expressed in 11 brain regions but poly(A)- messenger RNAs were found at much higher levels than poly(A)+ messenger RNAs in the cerebellum. Hybridization with five oligonucleotide and two complementary DNA probes, corresponding to different parts of the full-length trkC complementary DNA, revealed that the two poly(A)- transcripts may encode for receptors truncated in their extracellular and kinase intracellular domains. During ontogeny, poly(A)- trkC messenger RNAs were found at low amounts at prenatal and early postnatal ages with a drastic increase in the cerebellum at postnatal day 30. No poly(A)- transcript was identified for the trk B gene. In situ hybridization revealed that trkC messenger RNAs are expressed both in granular and Purkinje cells in the cerebellum. Northern blot on RNA extracted from mice mutant strains with degeneration of either granular or both granular and Purkinje cells suggested that poly(A)- and poly(A)+ trkC messenger RNAs are expressed within the same cells. We have demonstrated the existence of several trkC transcripts that differ both by their size and polyadenylation. This phenomenon could be of physiological relevance in regulating TrkC functions. To the best of our knowledge, this is an original feature for a mammalian gene expression. Studies focused on poly(A)- messenger RNAs could give rise to the identification of other genes expressed in a similar fashion.

Animals↗
PubMed1981

Polypeptides encoded by polyadenylated and non-polyadenylated messenger RNAs from normal and heat shocked HeLa cells.

There is an increased synthesis of proteins in the molecular weight region of 100,000 72,000-74,000 and 37,000 two hours after treatment of HeLa cells for 10 min at 45 degrees C. In vitro translation, using a rabbit reticulocyte cell-free protein synthesising system, of HeLa cell cytoplasmic RNA shows that the prominent 72,000-74,000 Mr heat shock protein band comprises seven polypeptide species (namely alpha d beta gamma delta epsilon zeta) and these polypeptides are directly encoded by both polyadenylated and nonpolyadenylated mRNA.

Animals↗
PubMed1981

Chinese hamster polyadenylated messenger ribonucleic acid: relationship to non-polyadenylated sequences and relative conservation during messenger ribonucleic acid processing.

We have further analyzed the metabolism of specific messenger ribonucleic acid (mRNA) sequences within the cytoplasmic and nuclear RNA of Chinese hamster ovary (CHO) cells by using a set of previously constructed complementary deoxyribonucleic acid (DNA) clones (Harpold et al., Cell 17:1025-1035, 1979) as specific molecular probes in a variety of RNA:DNA hybridization experiments. The majority of the labeled mRNA complementary to each of the nine clones was found in the polyribosomes, with some variation between individual sequences. The great majority of each specific mRNA labeled for 3 h or less was in the polyadenylated [poly(A)+] fraction. However, the amount of each sequence increased in the non-poly(A)+ [poly(A)-] fraction after very long label times, suggesting the derivation of the poly(A)- RNA from the poly(A)+ RNA. Eight of the nine mRNA's have cytoplasmic half-lives ranging from 8 to 14 h, whereas one of the mRNA's, the scarcest in the group, has a somewhat shorter half-life of approximately 3 h. The proportion of each of the specific long-lived mRNA's within the total labeled mRNA increased as a function of labeling time, indicating that a large fraction, probably greater than 50%, of the initially labeled poly(A)+ mRNA in CHO cells has a half-life of less than 3 h. A quantitative analysis of the kinetics of labeling of specific nuclear and cytoplasmic sequences indicated that a significant fraction of the mRNA sequences transcribed from genes containing these nine CHO sequences were successfully processed into mRNA. However, two of the CHO mRNA sequences were only partially conserved during nuclear processing to yield mRNA. These studies demonstrated that events at two post-transcriptional levels, differential nuclear processing efficiency of different primary transcripts and cytoplasmic stability of different mRNA's, can be involved in the determination of the cytoplasmic concentrations of different mRNA's.

Animals↗
PubMed1999

Utilization of splicing elements and polyadenylation signal elements in the coupling of polyadenylation and last-intron removal.

Polyadenylation (PA) is the process by which the 3' ends of most mammalian mRNAs are formed. In nature, PA is highly coordinated, or coupled, with splicing. In mammalian systems, the most compelling mechanistic model for coupling arises from data supporting exon definition (2, 34, 37). We have examined the roles of individual functional components of splicing and PA signals in the coupling process by using an in vitro splicing and PA reaction with a synthetic pre-mRNA substrate containing an adenovirus splicing cassette and the simian virus 40 late PA signal. The effects of individually mutating splicing elements and PA elements in this substrate were determined. We found that mutation of the polypyrimidine tract and the 3' splice site significantly reduced PA efficiency and that mutation of the AAUAAA and the downstream elements of the PA signal decreased splicing efficiency, suggesting that these elements are the most significant for the coupling of splicing and PA. Although mutation of the upstream elements (USEs) of the PA signal dramatically decreased PA, splicing was only modestly affected, suggesting that USEs modestly affect coupling. Mutation of the 5' splice site in the presence of a viable polypyrimidine tract and the 3' splice site had no effect on PA, suggesting no effect of this element on coupling. However, our data also suggest that a site for U1 snRNP binding (e.g., a 5' splice site) within the last exon can negatively effect both PA and splicing; hence, a 5' splice site-like sequence in this position appears to be a modulator of coupling. In addition, we show that the RNA-protein complex formed to define an exon may inhibit processing if the definition of an adjacent exon fails. This finding indicates a mechanism for monitoring the appropriate definition of exons and for allowing only pre-mRNAs with successfully defined exons to be processed.

HeLa Cells↗
PubMed1982

Newly formed mRNA lacking polyadenylic acid enters the cytoplasm and the polyribosomes but has a shorter half-life in the absence of polyadenylic acid.

Labeled adenovirus type 2 nuclear RNA molecules from cells treated with 3'-deoxyadenosine (3'dA) were earlier reported to lack polyadenylic acid [poly(A)], but to be correctly spliced in the nucleus (M. Zeevi et al., Cell 26:39-46, 1981). We have now found that the shortened mRNA molecules, lacking poly(A), can also be found in the cytoplasm of 3'dA-treated cells in association with the polyribosomes. In addition, the accumulation of labeled, nuclear adenovirus-specific RNA complementary to early regions 1a, 1b, and 2 of the adenovirus genome was approximately equal in 3'dA-treated and control cells. At the initial appearance of newly labeled adenovirus type 2 RNA (10 min) in the cytoplasm, there was one-half as much labeled RNA in 3'dA-treated cells as in the control. However, control cells accumulated additional mRNA in the cytoplasm very rapidly in the first 40 min of labeling, whereas the 3'dA-treated cells did not. Therefore, it appears that the correctly spliced, poly(A)- mRNA molecules that are labeled in the presence of 3'dA can be transported from the nucleus with nearly the same frequency and the same exit time as in control cells and can be translated in the cytoplasm but have a much shorter half-life than the poly(A)+ mRNA molecules from control infected cells. From these results it is suggested that the role of poly(A) may be entirely to increase the longevity of cytoplasmic mRNA.

Adenoviruses, Human↗