Hormone‐induced expression of the CHSl gene from Saccharomyces cerevisiae

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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. MATα 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.