Structural and functional analysis of the MAL1 locus of Saccharomyces cerevisiae.

Abstract

We describe the isolation of a 22.6-kilobase fragment of DNA containing the MALI locus of Saccharomyces cerevisiae. Our results demonstrate that the MALI locus, like the MAL6 locus, is a complex locus containing three genes. These genes were organized similarly to their MAL6 counterparts. We refer to them as MALI], MAL12, and MAL13 and show that they are functionally homologous to the MAL61 (encoding maltose permease), MAL62 (encoding maltase), and MAL63 (encoding the positive regulator) genes of the MAL6 locus. Transcription from each of the three genes was analyzed in a strain carrying the undisrupted MALI locus and in strains carrying single disruptions in each of the MALI genes. The MALI and MAL6 loci were found to be highly sequence homologous and conserved throughout the region containing these three genes. The strain used to isolate the MALI locus also carried the tightly linked SUCI gene. The SUCI gene was found to be located on the same 22.6-kilobase fragment containing the MALI locus and 5 kilobases from the 3' end of the MAL12 gene. The meaning of these results with regard to the mechanism of regulation of maltose fermentation is discussed.The fermentation of maltose by Saccharomyces spp. requires the presence of at least one of a series of five unlinked loci: MALI, MAL2, MAL3, MAI4, or MAL6 (1). Several standard maltose-fermenting laboratory strains have been genetically analyzed and shown to carry one dominant MAL locus and one or two additional, partially functional, MAL loci. Physical analysis of these strains revealed extensive sequence homology between the cloned MAL6 locus and the other MAL loci (7,17,18,23).The maltose-fermentative enzymes maltase and maltose permease are subject to both maltose induction and glucose repression. In the presence of maltose, both of these enzymes are induced approximately 30-fold, while in the noninduced state, only low basal levels of these enzymes are present (10,26). It has been postulated that a positive regulatory function is required for induction and that a gene encoding this regulatory function maps to each of the dominant MAL loci (28,29). More recent genetic analysis of maltose fermentation has revealed other functions encoded by the MAL loci which are required for fermentation (8, 11, lla, 14, 22; Chang et al., submitted for publication). Federoff et al. (13) cloned a segment of DNA from Saccharomyces carlsbergensis CB11 that was shown to contain the MAL6 locus (23). This cloned fragment contains three transcribed regions which we refer to as MAL61, MAL62, and MAL63 (22). All three genes are required for maltose fermentation. Gene disruption experiments at the MAL6 locus have confirmed these results (11; Chang et al., submitted). MAL63 has been shown to encode the positive regulatory gene product required for induction of maltase and maltose permease (Chang et al., submitted). Gene disruption experiments have shown that MAL62 is the structural gene encoding maltase (11). MAL61 is believed to code for maltose permease (9; Chang et al., submitted). Mut...

Molecular genetic study of introgression between Saccharomyces bayanus and S. cerevisiae

“…Each MAL locus is a complex of three genes: GENE1 encodes maltose permease, GENE2 encodes maltase and GENE3 encodes the MALactivator (Charron et al, 1989). All three functional genes are required for a strain to ferment maltose (Charron et al, 1986). However, in some cases only one or two of the three active genes are present and the strains are therefore not able to ferment maltose (Naumov et al, 1994b).…”

Expression Patterns of Genes and Enzymes Involved in Sugar Catabolism in IndustrialSaccharomyces cerevisiaeStrains Displaying Novel Fermentation Characteristics

“…The expression of the MALx1 and MALx2 genes required for maltose utilisation is often repressed in the presence of glucose 7,15,27,35 . This phenomenon has a negative effect on the early utilisation of maltose since glucose (10-15 g/L) and fructose (1-2 g/L) are initially present in an all-malt wort.…”

MAL11 and MAL61 encode the inducible high-affinity maltose transporter of Saccharomyces cerevisiae

“…Two kinetically different systems were identified: a high-affinity transporter with a Km of 4 mM and a low-affinity transporter with a Km of 70 to 80 mM. The high-affinity maltose transporter is maltose inducible and is encoded by the MALlI (and/or MAL61) (1,5,7,12,17,18). Each locus is a complex locus consisting of three genes essential for maltose fermentation (5,7,17,18).…”

“…The high-affinity maltose transporter is maltose inducible and is encoded by the MALlI (and/or MAL61) (1,5,7,12,17,18). Each locus is a complex locus consisting of three genes essential for maltose fermentation (5,7,17,18). GENE 1 has been suggested to encode maltose permease based on genetic analysis of mutations in MAL61, the GENE 1 located at the MAL6 locus (4).…”