RESUMEN
Conversion of a nascent precursor tRNA to a mature functional species is a multipartite process that involves the sequential actions of several processing and modifying enzymes. La is the first protein to interact with pre-tRNAs in eukaryotes. An opal suppressor tRNA served as a functional probe to examine the activities of yeast and human (h)La proteins in this process in fission yeast. An RNA recognition motif and Walker motif in the metazoan-specific C-terminal domain (CTD) of hLa maintain pre-tRNA in an unprocessed state by blocking the 5'-processing site, impeding an early step in the pathway. Faithful phosphorylation of hLa on serine 366 reverses this block and promotes tRNA maturation. The results suggest that regulation of tRNA maturation at the level of RNase P cleavage may occur via phosphorylation of serine 366 of hLa.
Asunto(s)
Autoantígenos/metabolismo , Precursores del ARN/metabolismo , ARN de Transferencia de Serina/química , ARN de Transferencia de Serina/genética , Ribonucleoproteínas/metabolismo , Schizosaccharomyces/genética , Serina , Autoantígenos/química , Secuencia de Bases , Humanos , Modelos Moleculares , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Conformación de Ácido Nucleico , Fosforilación , Fosfotirosina , Precursores del ARN/genética , Ribonucleoproteínas/química , Schizosaccharomyces/crecimiento & desarrollo , Factores de Transcripción/química , Factores de Transcripción/metabolismo , Antígeno SS-BRESUMEN
In order for RNA polymerase (pol) III to produce a sufficient quantity of RNAs of appropriate structure, initiation, termination, and reinitiation must be accurate and efficient. Termination-associated factors have been shown to facilitate reinitiation and regulate transcription in some species. Suppressor tRNA genes that differ in the dT(n) termination signal were examined for function in Schizosaccharomyces pombe. We also developed an S. pombe extract that is active for tRNA transcription that is described here for the first time. The ability of this tRNA gene to be transcribed in extracts from different species allowed us to compare termination in three model systems. Although human pol III terminates efficiently at 4 dTs and S. pombe at 5 dTs, Saccharomyces cerevisiae pol III requires 6 dTs to direct comparable but lower termination efficiency and also appears qualitatively distinct. Interestingly, this pattern of sensitivity to a minimal dT(n) termination signal was found to correlate with the sensitivity to alpha-amanitin, as S. pombe was intermediate between human and S. cerevisiae pols III. The results establish that the pols III of S. cerevisiae, S. pombe, and human exhibit distinctive properties and that termination occurs in S. pombe in a manner that is functionally more similar to human than is S. cerevisiae.
Asunto(s)
ARN Polimerasa III/fisiología , Schizosaccharomyces/genética , Transcripción Genética , Amanitinas/farmacología , ARN de Transferencia/genética , ARN de Transferencia/metabolismo , Saccharomyces cerevisiae/genética , Especificidad de la EspecieRESUMEN
BACKGROUND: We report on sixteen patients with a left ventricular aneurysm presenting at less than a month following myocardial infarction. METHODS: All patients had significant left anterior descending coronary artery disease, and in eight cases (50%), this was the only significant pathology. Two patients who were treated conservatively, died within three months of infarction. RESULTS: Of the fourteen surgically treated patients, one died. There have been two late deaths, one at ten months and the other at four years postinfarction. Patients who present early after infarction, usually have a large anterior aneurysm, requiring early surgical repair with ventricular aneurysmectomy and revascularization. This group of patients showed a higher risk for major complications (such as thrombo-embolism, arrhythmias) and/or death. Emergency coronary artery bypass surgery may prove beneficial in the prevention of aneurysm formation by revascularizing the viable but ischemic tissue in that area.