TRANSCRIPTIONAL REGULATION OF SUP35 AND SUP45 IN SACCHAROMYCES-CEREVISIAE

SUP35 and SUP45 encode translational release factors in the yeast Sacc haromyces cerevisiae. In addition, Sup35p is related to the cytoplasmi cally inherited prion-like phenotype [PSI+]. The vital cellular role o f Sup35p and Sup45p prompted us to study the regulation of transcripti on of the corresponding genes. Since the [PSI] state of the yeast stra in affects the abundance of Sup35p and Sup45p, both [PSI+] and [psi(-) ] variants were included in these analyses. It turned out that SUP35 a nd SUP45 transcript levels are regulated by nutritional changes and st ress in a way strikingly similar to those of ribosomal protein genes. The [PSI] state did not influence the respective transcript levels nor their regulation, although HSP12 (as a monitor of general stress-resp onsive) gene expression appeared to differ in the two variant strains. The transcription activation sites of SUP35 and SUP45 were mapped usi ng deletion analysis of the respective promoter-reporter fusion genes. The UAS in both cases was found to consist of an Abflp-site and a T-r ich element. Also in this respect SUP35 and SUP45 show a notable resem blance with ribosomal protein genes. Evidence was found that SUP35 in addition harbors a potential internal promoter element which became ac tive after progressive 5'-deletion removing the first of the three in- frame ATGs. (C) 1997 John Wiley & Sells, Ltd.