[Intra-alveolar hemorrhages disclosing Wegener disease with hepatic involvement].
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A Lescure
Publications and source records attributed to A Lescure.
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↗
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↗
mRNA nuclear export.
The export of mRNA from the nucleus to the cytoplasm is an essential step in the expression of genetic information in eukaryotes. It is an energy-dependent process and involves transport across the nuclear pores. It requires both cis-acting ribonucleoprotein particle signals and specific trans-acting factors. Although much remains to be learned, recent information has begun to define this pathway at both the cellular and biochemical levels and indicates that it is used as a key regulatory step by several viruses.
Animals↗
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↗
The proximal promoter and the start site cooperate to specify correct U1 snRNA transcription initiation by RNA polymerase II.
In this work, we attempted to gain insight into the detailed mechanism allowing correct transcription initiation of U1 snRNA genes by RNA polymerase II. Abolition of the CA motif residing at -1/+1 in the Xenopus U1 gene leads to a loss of the ability of the promoter to direct accurate initiation. A discrete site is selected only if a purine preceded by a pyrimidine is positioned at 58/57 bp downstream of the center of the PSE. The PSE alone is unable to designate a discrete initiation site. Rather, it serves to set the location of an initiation window without discriminating suitable from unsuitable initiation sites. The latter role is devoted to a PyPu sequence positioned at -1/+1. Therefore, it is the concomitant action of the PSE and an essential PyPu positioned at the proper distance from this promoter that specifies correct U1 snRNA transcription initiation by RNA polymerase II.
Animals↗
The different positioning of the proximal sequence element in the Xenopus RNA polymerase II and III snRNA promoters is a key determinant which confers RNA polymerase III specificity.
We and others have previously described the TATA motif as a major determinant for Pol III specificity of the U6 promoter. Surprisingly, however, the data documented here show that the sole introduction of a TATA sequence into a U1 Pol II snRNA gene is not sufficient to confer Pol III transcription. Rather, this promoter element can mediate optimal Pol III transcription only if the PSE, the second promoter element, is shifted 4 bp upstream of the position it occupies in Pol II snRNA genes. As a result, the PSE-TATA-start site spacing introduced into the U1 Pol II gene is identical to that of the U6 gene and is strictly required to produce properly initiated Pol III transcripts. Thus, Pol II and Pol III PSEs, although similar in sequence, are not positionally equivalent. Competitive experiments raise the possibility that vertebrate U6 genes contain other, as yet unidentified, promoter elements.
Animals↗