The SNF2/SWI2/GAM1/TYE3/RIC1 gene is involved in the coordinate regulation of phospholipid synthesis in Saccharomyces cerevisiae.

Genes involved in the phospholipid synthesis of Saccharomyces cerevisiae, such as PEM1, PEM2, PSS, and INO1, are coordinately repressed by myo-inositol and choline. In order to investigate this regulation, we transformed wild-type yeast with a PEM1 promoter-lacZ fusion and isolated two mutants, named ric1 and ric2 (regulation by myo-inositol and choline), exhibiting decreased PEM1 expression. The lowered PEM1 expression in the mutants was monitored in colonies in terms of their failure fully to develop blue color on 5-bromo-4-chloro-3-indolyl-beta-galactopyranoside-containing agar. ric1 mutant was auxotrophic for myo-inositol, indicating that INO1 expression was also affected, whereas ric2 mutant required myo-inositol only in the presence of choline. The RIC1 gene was isolated by complementation of the Ino- phenotype of ric1 mutant and its identity was confirmed by genetic cross between the original ric1 mutant and a gene disruptant. The RIC1 gene was sequenced and found to be identical with the previously identified gene, SNF2/SWI2/GAM1/TYE3, which is known to encode a general transcription factor required for the expression of various genes including INO1. Analysis using various lacZ fusion constructs containing promoters for genes in phospholipid synthesis revealed that the expression of myo-inositol-choline-regulated genes, PEM1, PEM2, PSS, CKI, and INO1, was markedly decreased in the snf2/swi2/gam1/tye3/ric1 background, but the expression of a constitutive gene, PIS, was not. We conclude that SNF2/SWI2/GAM1/TYE3/RIC1 is a positive regulatory gene required for the expression of not only INO1 gene, but also of myo-inositol-choline-regulated genes in general.