Hormone‐induced expression of the CHSl gene from Saccharomyces cerevisiae

Abstract

When MATa cells of Saccharomyces cerevisiae have been treated with the mating hormone α‐factor an increase in chitin synthase zymogen, as well as chitin content in the cell‐wall fraction, have been reported. With a DNA probe derived from the cloned CHSl gene that codes for chitin synthase I [Bulawa, C. E., Slater, M., Cabib, E., Au‐Young, J., Sburlati, A., Adair, W. L. and Robbins, P. (1986) Cell 46 , 213–225] a Northern analysis was conducted of CHSl ‐specific transcripts. α‐Factor‐treated MATa cells revealed more than sixfold elevated steady‐state levels of CHSl mRNA as compared to control cells. MAT α cells responded the same way when treated with a‐factor although induction rate was somewhat smaller. After hormone application a rapid increase in CHSl mRNA levels could be observed that occurred also in the absence of ongoing protein synthesis. In order to minimize possible side effects of CHSl ‐coding sequences on expression and mRNA stability a CHSl::SUC2 chimaeric gene was constructed where 730 bp of the CHSl promoter region (+ 20 bp of the coding region) were fused in frame to a fragment of the SUC2 coding region. The fusion protein exhibits invertase activity that has been used to monitor CHSl promoter activity. By analysis of shortened versions of the CHSl promoter a 94‐bp DNA fragment has been identified that confers hormone inducibility to the CHSl promoter. According to the published sequence of the CHSl gene, this fragment contains four repeats of a TGAAACA consensus sequence previously identified in the α‐factor‐inducible BARl promoter [Kronstad, J. W., Holly, J. A. and MacKay, V. L. (1987) Cell 50 , 369–377]. This heptamer may represent the cis ‐acting element involved in mating‐hormone‐mediated gene expression in yeast.