Characterization of two new genes down-regulated by alpha-factor.

To detect genes directly down-regulated by alpha-factor, 55,000 plaque-forming units of a Saccharomyces cerevisiae lambda gt10 gene bank were differentially screened with cDNA of cells treated with alpha-factor for 20 min. Two new genes were detected in this way, called alpha0.5 and alpha0.6. The former is transiently down-regulated by alpha-factor; it is very highly transcribed in late exponential-phase cells. The gene, located on the right arm of chromosome XIII, codes for a 59 amino-acid protein with a signal peptide. The protein has been shown with an antibody to be present in the membrane fraction. The gene has also been cloned as HOR7 (hyperosmolarity-responsive protein; Hirayama et al., 1995). No other homologous sequences have been detected in the yeast genome. alpha0.6, located on the right arm of chromosome XII, corresponds to the open reading frame YLR110c; it codes for a 133 amino-acid protein containing a signal peptide. Its derived amino-acid sequence is homologous to the N-terminal half of the SED1 gene product. SED1, when overexpressed, is able to suppress a defect in the HDEL receptor coded for by the ERD2 gene (Hardwick and Pelham, 1994); however, alpha0.6 is not able to do so. The disruption of alpha0.5 or alpha0.6 does not lead to a special phenotype.