REGULATION OF MALTOSE UTILIZATION IN SACCHAROMYCES-CEREVISIAE BY GENES OF THE RAS PROTEIN-KINASE-A PATHWAY

In Saccharomyces cerevisiae maltose utilization requires a functional MAL locus, each composed of three genes: MALR (gene 3) encoding a regu latory protein, MALT (gene 1) encoding maltose permease and MALS (gene 2) encoding maltase, We show that constitutive activation of the RAS/ protein kinase A pathway severely reduces growth of MAL1 strains on m altose, This may be a consequence of reduction in MALT mRNA, reduced V -max and increased catabolite inactivation of the MALT-encoded maltose transporter in the MAL1 strain, Mutations in the GGS1/TPS1 gene, whic h restricts glucose influx and possibly affects signalling, relieve ca rbon catabolite repression on both maltase and maltose permease and re duce maltose permease inactivation.