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A Krol

Publications and source records attributed to A Krol.

At least 73 records · Page 4Linked to original sources
PubMed1994

Common structural features of the Ro RNP associated hY1 and hY5 RNAs.

The secondary structures of human hY1 and hY5 RNAs were determined using both chemical modification techniques and enzymatic structure probing. The results indicate that both for hY1 and for hY5 RNA the secondary structure largely corresponds to the structure predicted by sequence alignment and computerized energy-minimization. However, some important deviations were observed. In the case of hY1 RNA, two regions forming a predicted helix appeared to be single-stranded. Furthermore, the pyrimidine-rich region of hY1 RNA appeared to be very resistant to reagents under native conditions, although it was accessible to chemical reagents under semi-denaturing conditions. This may point to yet unidentified tertiary interactions for this region of hY1 RNA. In the case of hY5 RNA, two neighbouring internal loops in the predicted structure appeared to form one large internal loop.

Animals↗
PubMed1994

Eukaryotic selenocysteine inserting tRNA species support selenoprotein synthesis in Escherichia coli.

Although the tRNA species directing selenocysteine insertion in prokaryotes differ greatly in their primary structure from that of their eukaryotic homologues they share very similar three-dimensional structures. To analyse whether this conservation of the overall shape of the molecules reflects a conservation of their functional interactions it was tested whether the selenocysteine inserting tRNA species from Homo sapiens supports selenoprotein synthesis in E. coli. It was found that the expression of the human tRNA(Sec) gene in E.coli can complement a lesion in the tRNA(Sec) gene of this organism. Transcripts of the Homo sapiens and Xenopus laevis tRNA(Sec) genes synthesised in vitro were amino-acylated by the E.coli seryl-tRNA ligase although at a very low rate and the resulting seryl-tRNA(Sec) was bound to and converted into selenocysteyl-tRNA(Sec) by the selenocysteine synthase of this organism. Selenocysteyl-tRNA(Sec) from both eukaryotes was able to form a complex with translation factor SELB from E.coli. Although the mechanism of selenocysteine incorporation into seleno-proteins appears to be rather different in E.coli and in vertebrates, we observe here a surprising conservation of functions over an enormous evolutionary distance.

Animals↗
PubMed1994

Base modification pattern at the wobble position of Xenopus selenocysteine tRNA(Sec).

We examined the base modification pattern of Xenopus tRNA(Sec) using microinjection into Xenopus oocytes, with particular focus on the wobble base U34 at the first position of the anticodon. We found that U34 becomes modified to mcm5U34 (5-methylcarboxymethyluridine) in the oocyte cytoplasm in a rather complex manner. When the tRNA(Sec) gene is injected into Xenopus oocyte nuclei, psi 55 and m1A58 are readily obtained, but not mcm5U34. This will appear only upon cytoplasmic injection of the gene product arising from the first nuclear injection. In contrast, tRNA(Sec) produced by in vitro transcription with T7 RNA polymerase readily acquires i6A37, psi 55, m1A58, and mcm5U34. The latter is obtained after direct nuclear or cytoplasmic injections. It has been reported by others that mcm5Um, a 2'-O-methylated derivative of mcm5U34, also exists in rat and bovine tRNA(Sec). With both the gene product and the in vitro transcript, and using the sensitive RNase T2 assay, we were unable to detect under our conditions the presence of a dinucleotide carrying mcm5Um and that would be therefore refractory to hydrolysis. We showed that the unusual mcm5U acquisition pathway does not result from impairment of nucleocytoplasmic transport. Rather, these data can be interpreted to mean that the modification is performed by a tRNA(Sec) specific enzyme, limiting in the oocyte cytoplasm.

Animals↗
PubMed1994

[Survival of patients following the diagnosis of AIDS in the Amsterdam region, 1982-1991].

OBJECTIVE: To evaluate the survival of 975 AIDS patients diagnosed in the Amsterdam region between 1982 and 1991, with follow-up until December 31st, 1992. METHODS: Analysis of data from the active AIDS surveillance system for the Amsterdam region at the Municipal Health Service. RESULTS: Amsterdam region residents had 1, 2 and 3-year survivals of 69.8%, 42.6% and 21.2%, respectively. The 5-year survival was 7.7%. The median survival probability for all patients showed great improvement, from 9 months in 1982-1985 to 26 months in 1990. For patients initially presenting with only Pneumocystis carinii pneumonia (PCP) the greatest improvement occurred between the period 1982-1985 and the year 1986. For patients without PCP the most important improvement occurred one year later. From 1988 onwards no important improvement in the 1-year survival is noticed. The 2-year survival, however, appears still to be increasing. In a Cox proportional hazards model the following variables were found to be independent predictors for survival: age at diagnosis, earliest clinical AIDS manifestations, year of diagnosis and HIV risk group. No differences were seen in the 1 and 2-year survival probabilities for men and women with AIDS. Heterosexual men and women tended to have a poorer survival than intravenous drug users and homosexual and bisexual men. CONCLUSION: A noticeable improvement in the survival probability with time occurred for AIDS patients living in the Amsterdam region through the years 1982-1991, although the overall survival after AIDS diagnosis is still poor. The 1-year survival appears to have reached a plateau, the 2-year survival is still increasing. Improved clinical experience, awareness of HIV related complaints in high risk groups, better diagnostic methods and the availability of proper medication (prophylactic and treatment) are the most likely explanations of the improvement in survival.

AIDS-Related Opportunistic Infections↗
PubMed1994

The N-terminal domain of the human TATA-binding protein plays a role in transcription from TATA-containing RNA polymerase II and III promoters.

In eukaryotes, the TATA box binding protein (TBP) is an integral component of the transcription initiation complexes of all three classes of nuclear RNA polymerases. In this study we have investigated the role of the N-terminal region of human TBP in transcription initiation from RNA polymerase (Pol) I, II and III promoters by using three monoclonal antibodies (mAbs). Each antibody recognizes a distinct epitope in the N-terminal domain of human TBP. We demonstrate that these antibodies differentially affect transcription from distinct classes of promoters. One antibody, mAb1C2, and a synthetic peptide comprising its epitope selectively inhibited in vitro transcription from TATA-containing, but not from TATA-less promoters, irrespective of whether they were transcribed by Pol II or Pol III. Transcription by Pol I, on the other hand, was not affected. Two other antibodies and their respective epitope peptides did not affect transcription from any of the promoters tested. Order of addition experiments indicate that mAb1C2 did not prevent binding of TBP to the TATA box or the formation of the TBP-TFIIA-TFIIB complex but rather inhibited a subsequent step of preinitiation complex formation. These data suggest that a defined region within the N-terminal domain of human TBP may be involved in specific protein-protein interactions required for the assembly of functional preinitiation complexes on TATA-containing, but not on TATA-less promoters.

Antibodies, Monoclonal↗
PubMed1994

Transcription factors required for the expression of Xenopus laevis selenocysteine tRNA in vitro.

It has previously been reported that transcription in vivo of the tRNA(Sec) gene requires three promoter elements, a PSE and a TATA-box upstream of the coding region which are functionally interchangeable with the U6 snRNA gene counterparts and an internal B-block, resembling that of classical tRNA genes (1). We have established an in vitro transcription system from HeLa cells in which three factors, which are either essential for or stimulate transcription were identified. Apart from the TATA-binding protein TBP, the PSE-binding protein PBP was found to be essentially required for expression of the gene. Depletion of PBP from cell extracts by PSE-oligonucleotides abolished tRNA(Sec) transcription, which could be reconstituted by readdition of partially purified PBP. Addition of increasing amounts of recombinant human TBP to an S100 extract stimulated transcription of the tRNA(Sec), the mouse U6 snRNA and the human Y3 genes, an effect which was not observed in the case of a TATA-less tRNA gene. Purified human TFIIA strongly stimulated tRNA(Sec) transcription in a fashion depending on the concentration of TBP. Surprisingly, partially purified TFIIIC was shown to be dispensable for transcription in vitro and unable to bind the B-block of this gene in vitro, although its sequence matches the consensus for this element. Collectively, these data suggest that the mechanism by which transcription complexes are formed on the tRNA(Sec) gene is dramatically different from that observed for classical tRNA genes and much more resembles that observed for externally controlled pol III genes.

Animals↗
PubMed1994

Characteristics of long-term asymptomatic infection with human immunodeficiency virus type 1 in men with normal and low CD4+ cell counts.

From a cohort study of homosexual men in Amsterdam, 61 human immunodeficiency virus (HIV)-infected men who had remained asymptomatic for at least 7 years were identified. In a nested case control study, these men were compared with 142 men who progressed symptomatic HIV infection (CDC class IV) within 7 years, regarding laboratory markers, sexual behavior, psychologic coping, and drug use. Of the 61 long-term asymptomatic men, 13 had a CD4+ cell count > or = 500/mm3 after 7 years; in 2 of these 13, the CD4+ cell count had not declined during follow-up. Independent of CD4+ cell count, long-term asymptomatic HIV-1 infection was characterized by stable T cell reactivity after stimulation with monoclonal CD3 antibodies, seropositivity for antibodies to HIV core proteins, and the absence of hepatitis B markers. No association with markers of high-risk sex or the recreational use of drugs was found. Long-term asymptomatic men had a slightly lower score regarding the coping behavior active problem-solving; no other associations with coping behaviors were found.

Adult↗
PubMed1994

Predictors of disease progression in HIV-infected homosexual men with CD4+ cells < 200 x 10(6)/l but free of AIDS-defining clinical disease.

OBJECTIVE: To study progression of HIV infection in individuals who are free of AIDS-defining clinical disease with CD4+ cell counts < 200 x 10(6)/l. DESIGN: Prospective and nested case-control study. SETTING: Amsterdam cohort study on HIV infection, The Netherlands. PARTICIPANTS: Prospective study: 148 asymptomatic HIV-infected individuals with < 200 x 10(6)/l CD4+ cells. Nested case-control study: 58 men with AIDS-free follow-up more than 2 years after CD4 count < 200 x 10(6)/l, compared with 63 who progressed to AIDS within 2 years. MAIN OUTCOME MEASURES: Progression to AIDS according to the 1987 Centers for Disease Control and Prevention case definition and death. RESULTS: Median AIDS-free interval was 22 months, median interval to death 41 months. Presence of syncytium-inducing (SI) HIV variants, HIV p24 antigen, and a low T-cell response after stimulation with phytohaemagglutinin (PHA) were independent predictors of progression to AIDS. Probability of 1 year AIDS-free survival varied between 89 and 38% by the presence or absence of these additional markers. Effect of early treatment could only be detected in men with HIV p24 antigen and SI variants. Case-control analysis showed similar changes over time regarding prognostic markers in both groups although at a lower rate in the AIDS-free men. Eight men remained AIDS-free more than 4 years, SI variants were absent in seven, and all eight were p24-seronegative. CONCLUSIONS: HIV-infected individuals can remain disease-free for more than 4 years with very low CD4+ cell counts, provided that they lack other progression markers: SI variants, p24 antigen and a low PHA-induced T-cell reactivity. A beneficiary effect of early treatment may be limited to men with SI variants and/or p24 antigen.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Effects of the carbohydrase inhibitor miglitol in sulfonylurea-treated NIDDM patients.

OBJECTIVE: To examine the effects of the carbohydrase inhibitor miglitol (BAY m 1099) on the metabolic profiles of non-insulin-dependent diabetes mellitus (NIDDM) patients suboptimally controlled on maximal daily doses of sulfonylurea (SFU) agents. RESEARCH DESIGN AND METHODS: Multicenter, double-blind, randomized, placebo-controlled 14-week clinical trial with six-week, single-blind placebo lead-in and run-out periods. NIDDM volunteers (192) with fasting plasma glucose (FPG) 140-250 mg/dl and hemoglobin A1c (HbA1c) 6.5-12.0% after at least 4 weeks of treatment with SFU at maximal dose were stratified by baseline HbA1c (above and below 9.0%) and then randomly assigned within strata to placebo (n = 63), 50 mg miglitol 3 times a day (n = 61), or 100 mg miglitol 3 times a day (n = 68). Efficacy was assessed by HbA1c, FPG, insulin, and lipid concentrations, and by plasma glucose and serum insulin responses to a standard meal. RESULTS: In the 50 and 100 mg miglitol treatment groups, the mean changes from baseline in HbA1c (with placebo values subtracted) were 0.82 and 0.74%, respectively, and were highly significant (P = 0.0001 in each case). Mean peak plasma glucose levels after a standard test meal were comparably lowered by 57 mg/dl with the 50 mg miglitol dose, and by 64 mg/dl with the 100 mg miglitol dose compared with placebo (P = 0.0001 for each), with associated reductions in integrated serum insulin response (P < 0.05). No significant drug-associated changes in FPG, insulin, or cholesterol levels were noted, but fasting triglyceride levels were lowered significantly with the 50 mg miglitol dose. Miglitol's side effects were limited to flatulence, loose stools, and abdominal discomfort, which were dose-related, rapidly resolved on drug discontinuation, and led to withdrawal from the study of 5 and 15% of patients taking 50 and 100 mg miglitol, respectively. CONCLUSIONS: Miglitol may be indicated as effective adjuvant therapy in NIDDM patients with suboptimal metabolic control despite conventional treatment with diet and maximal daily doses of SFU. The dose of 50 mg miglitol 3 times a day may be preferable to 100 mg miglitol 3 times a day because of comparable efficacy and substantially reduced side effects.

1-Deoxynojirimycin↗
PubMed1993

Point mutations 5' to the tRNA selenocysteine TATA box alter RNA polymerase III transcription by affecting the binding of TBP.

The selenocysteine tRNA(Sec) gene possesses two external promoter elements, one of which is constituted by a strong TATA box. Point mutant analysis performed in this study led to the conclusion that the functional TATA promoter actually encompasses the sequence -34 GGGTATAAAAGG-23. Individual changes at T-31 do not affect transcription much. Position T-29 is less permissive to mutation since transversion to a G, for example, is less well tolerated than at T-31. Interestingly, a double point mutation, converting GG(-33/-32) to TT, causes abrogation of transcription in vivo and severe reduction of transcription in vitro with human TBP. Therefore, data obtained underscore the fact that, in the Xenopus tRNA(Sec), these two Gs are an integral part of the TATA promoter. Gel retardation experiments indicate that the GG to TT substitution, which led human TBP to lose its ability to support efficient transcription in vitro, correlates with the appearance of an altered pattern of retarded complexes. Altogether, the data presented in this report support a model in which TBP interacts directly with the TATA element of the tRNA(Sec) gene, in contrast to the type of interaction proposed for classical TATA-less tRNA genes.

Animals↗
PubMed1993

Promoter strength and structure dictate module composition in RNA polymerase III transcriptional activator elements.

RNA polymerase III transcription of genes with external promoters only (e.g. U6 snRNA) or containing in addition an internal B box (selenocysteine tRNA(Sec)) is stimulated by upstream elements; a distal sequence element (DSE) for U6 or an activator element in the tRNA(Sec) gene. In contrast to the composite structure of the DSE which requires an octamer motif, the Xenopus tRNA(Sec) activator element contains an SPH motif only. In vivo transcription is optimally stimulated by SPH in an absolute octamer-independent manner since adding octamer does not induce superstimulation. Experiments performed in the work presented here led to the following observations. Co-operation between SPH and octamer motifs can be detected in two distinct cases: first when these motifs are placed in front of B box-less tRNA(Sec) or U6 external promoters and second, if either element of the external promoter (proximal sequence element or TATA element), or the SPH motif itself, are altered. Altogether, our data provide evidence that an SPH motif can function alone in an optimized promoter only. In contrast, an octamer becomes indispensable when the basal promoter is weak or disabled. It follows that module composition of Pol III transcriptional activator elements is dependent on the structure and strength of the promoter. This reveals the existence of cross-talk between activator and promoter elements, mediated by the bound transcription factors, which are thus able to compensate for each other in order to allow successful assembly of the transcription complex.

Animals↗
PubMed1993

Unique secondary and tertiary structural features of the eucaryotic selenocysteine tRNA(Sec).

Cotranslational insertion of selenocysteine into selenoenzymes is mediated by a specialized transfer RNA, the tRNA(Sec). We have carried out the determination of the solution structure of the eucaryotic tRNA(Sec). Based on the enzymatic and chemical probing approach, we show that the secondary structure bears a few unprecedented features like a 9 bp aminoacid-, a 4 bp thymine- and a 6 bp dihydrouridine-stems. Surprisingly, the eighth nucleotide, although being a uridine, is base-paired and cannot therefore correspond to the single-stranded invariant U8 found in all tRNAs. Rather, experimental evidence led us to propose that the role of the invariant U8 is actually played by the tenth nucleotide which is an A, numbered A8 to indicate this fact. The experimental data therefore demonstrate that the cloverleaf structure we derived experimentally resembles the hand-folded model proposed by Böck et al (ref. 3). Using the solution data and computer modelling, we derived a three-dimensional structure model which shows some unique aspects. Basically, A8, A14, U21 form a novel type of tertiary interaction in which A8 interacts with the Hoogsteen sites of A14 which itself forms a Watson-Crick pair with U21. No coherent model containing the canonical 15-48 interaction could be derived. Thus, the number of tertiary interactions appear to be limited, leading to an uncoupling of the variable stem from the rest of the molecule.

Animals↗
PubMed1993

Case report of Darier disease localized to the vulva in a 5-year-old girl.

A 5-year-old girl with Darier disease had numerous verrucous papules coalescing into plaques on both labia majora of approximately one year's duration. She was diagnosed as having genital warts, raising the suspicion of sexual abuse. Subsequently, a biopsy specimen from one of the vulvar lesions revealed histologic characteristics consistent with a diagnosis of Darier disease. The case is unusual for the age of onset and the site of initial involvement, and stresses the importance of including acantholytic disorders such as Darier disease in the differential diagnosis of a child with clinically verrucous lesions.

Biopsy↗
PubMed1993

A double-blind, placebo-controlled study comparing the efficacy and safety of ipsapirone versus lorazepam in patients with generalized anxiety disorder: a prospective multicenter trial.

This multicenter, double-blind, placebo-controlled, randomized study compared the efficacy, safety, and tolerability of ipsapirone (an azapirone anxiolytic) at daily dose levels of 10.0 to 30.0 mg with a daily dose of 2.0 to 6.0 mg of lorazepam (a benzodiazepine) or placebo when given to outpatients with generalized anxiety disorder (GAD) of moderate or greater severity. A total of 317 outpatients with a primary diagnosis of GAD according to DSM-III criteria (at least 1 month's duration) were randomized. Study entry criteria at the time of screening and at baseline included a Hamilton Rating Scale for Anxiety (HAM-A) score of 18 or more, a Covi Anxiety Scale score of 8 or more, and a Raskin Depression Scale score of 7 or less. The study design consisted of a 1-week, single-blind placebo evaluation, a 4-week, double-blind acute treatment period, and a 4-week extension period, followed by a 2-week, single-blind placebo withdrawal period. Efficacy was measured by changes in the HAM-A and Clinical Global Impression Scale and by evaluations of the Hamilton Rating Scale for Depression and Zung-Anxiety Self-Rating scale. The Raskin and Covi scales were performed at screening and baseline only. Withdrawal reactions were assessed during the withdrawal period by the Physician Withdrawal Checklist and by a patient self-rating checklist. Two-hundred sixty-three patients were valid for the analysis of efficacy in the ipsapirone (N = 87), lorazepam (N = 89), and placebo (N = 87) groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

A factor with Sp1 DNA-binding specificity stimulates Xenopus U6 snRNA in vivo transcription by RNA polymerase III.

We have previously shown that transcription of the Xenopus U6 snRNA gene by RNA polymerase III is stimulated in injected Xenopus oocytes by an activator element termed the DSE, which contains an octamer sequence. Data presented here reveal that the DSE contains, in addition, a GC-rich sequence capable of binding Sp1. Both elements are required to obtain wild-type levels of U6 transcription in vivo. The Xenopus U6 DSE exhibits optimal activation properties only when positioned at its normal location upstream from the start site. The U6 Sp1 motif binds the mammalian Sp1 transcriptional activator independently of the Oct-1 protein in vitro. Those mutations that lead to a reduced transcription level in vivo abolish the binding of Sp1 in vitro. Thus, transcriptional stimulation through the Xenopus U6 Sp1 motif is likely to be mediated by a protein with DNA-binding specificity identical to mammalian Sp1. These findings support the notion that RNA polymerase II and III transcription complexes share transactivators.

Animals↗