RESUMEN
Previous investigations into the mechanisms that control RNA Polymerase (Pol) I transcription have primarily focused on the process of transcription initiation, thus little is known regarding postinitiation steps in the transcription cycle. Spt4p and Spt5p are conserved throughout eukaryotes, and they affect elongation by Pol II. We have found that these two proteins copurify with Pol I and associate with the rDNA in vivo. Disruption of the gene for Spt4p resulted in a modest decrease in growth and rRNA synthesis rates at the permissive temperature, 30 degrees C. Furthermore, biochemical and EM analyses showed clear defects in rRNA processing. These data suggest that Spt4p, Spt5p, and, potentially, other regulators of Pol I transcription elongation play important roles in coupling rRNA transcription to its processing and ribosome assembly.
Asunto(s)
Proteínas Cromosómicas no Histona/metabolismo , Proteínas Nucleares/metabolismo , ARN Polimerasa II/metabolismo , ARN Polimerasa I/metabolismo , Procesamiento Postranscripcional del ARN , ARN Ribosómico/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Transcripción Genética , Factores de Elongación Transcripcional/metabolismo , Proteínas Cromosómicas no Histona/genética , Eliminación de Gen , Microscopía Electrónica , Mutación/genética , Proteínas Nucleares/genética , Unión Proteica , ARN Ribosómico/genética , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/ultraestructura , Proteínas de Saccharomyces cerevisiae/genética , Factores de Elongación Transcripcional/genéticaRESUMEN
Ischemic contracture of the left ventricle ("stone heart") was studied utilizing a previously described stone heart model. Our studies suggest that beta-adrenergic blockade is not quantitatively as important as hypothermia in protecting ischemic myocardium. On the basis of reduced fibrillatory activity and a slight protective effect shown by electron microscopy, it would appear that combining propranolol with hypothermia may be superior to either used singly.
