Induction of the 4-aminobutyrate and urea-catabolic pathways in Saccharomyces cerevisiae. Specific and common transcriptional regulators.

In the yeast Saccharomyces cerevisiae, induction of the 4-aminobutyrate-catabolic pathway by 4-aminobutyrate requires two positive regulatory factors, encoded by the UGA3 and the UGA35 genes respectively. In addition to this, expression of one gene of this pathway, namely the UGA4 gene encoding the 4-aminobutyrate-specific permease, is controlled negatively by the product of the UGA43 gene [Vissers, S., André, B., Muyldermans, F. & Grenson, M. (1989) Eur. J. Biochem. 181, 357-361]. We show here that the products of two of these regulatory genes, UGA35 and UGA43, also control the expression of the genes encoding the urea-catabolic pathway, although the 4-aminobutyrate and urea-catabolic pathways are synthesised under specific conditions and do not share any enzymatic step or metabolite: the UGA35 pathways are synthesised under specific conditions and do not share any enzymatic step or metabolite: the UGA35 gene is shown to be identical to the DURL gene which was previously identified as a positive regulatory factor of the urea-catabolic pathway; the UGA43 gene product is shown to behave like a negative regulatory factor of this pathway. In contrast to UGA35/DURL and UGA43, the positive regulatory factors encoded by the UGA3 gene and the previously identified DURM gene specifically control 4-aminobutyrate and urea catabolisms respectively. Northern hybridization experiments suggest that the UGA35/DURL and UGA43 common regulatory factors act at the transcriptional level. Our results show that the expression of two biochemically distinct nitrogenous catabolisms, as triggered by their respective inducers, seems to involve multiple regulatory factors, some of which are common to the two catabolic pathways.