Structure of the multigene family of MAL loci in Saccharomyces

Abstract

Multigene families are a ubiquitous feature of eukaryotes; however, their presence in Saccharomyces is more limited. The MAL multigene family is comprised of five unlinked loci, MAL1, MAL2, MAL3, MAL4 and MAL6, any one of which is sufficient for yeast to metabolize maltose. A cloned MAL6 locus was used as a probe to facilitate the cloning of the other four functional loci as well as two partially active alleles of MAL1. Each locus could be characterized as a cluster of three genes, MALR (regulatory), MALT (maltose transport or permease) and MALS (structural or maltase), encoded by a total of about 7 kb of DNA; however, homologous sequences at each locus extend beyond the coding regions. Our results indicate that there is extensive homology among the MAL loci, especially within their maltase genes. The greatest sequence diversity occurs in their regulatory gene regions. Southern cross analyses of the cloned MAL loci indicate a single duplication of the MAL6R-homologous sequences upstream of the MAL6R gene as well as an extensive duplication of more than 10 kb at the MAL3 locus. The large repeat at the MAL3 locus results in the presence of four copies of MAL3R-homologous sequences and two copies of MAL3T-homologous sequences at that locus. Two naturally occurring inactive alleles of MAL1 show a deletion or divergence of their MALR sequences. The significance of these repeats in the evolution of the MAL multigene family is discussed.

Genome sequence of the lignocellulose-bioconverting and xylose-fermenting yeast Pichia stipitis

“…Adjacent to MAL3 is MAL5, which is adjacent to YIC1, an a-glucosidase. Flanking this complex are a fungal transcriptional regulatory protein, SUC1.2, similar to MAL-activator proteins 25 , and a second putative fungalspecific regulatory protein, SUC1.4. Elsewhere in the genome, on chromosome 6, the a-glucosidase, MAL8, is immediately adjacent to the maltose permease, MAL4.…”

Identification and Characterization of a Novel Biotin Biosynthesis Gene inSaccharomyces cerevisiae

“…It is noteworthy that the original BIO6 gene of K7 is located in the subtelomeric region of chromosome II. Genes in the subtelomeric regions of chromosomes are often remodeled by chromosome rearrangements including recombination (18) and duplication (6). We hypothesize that the copy number of the BIO6 gene was increased by chromosomal rearrangements, reaching at least eight copies for K7 (diploid cells) to synthesize enough biotin in the sake mash.…”

Genome-wide analysis of maltose utilization and regulation in aspergilli

“…Among these genes, 10 protein-encoding genes were functionally annotated and involved in polysaccharide and disaccharide metabolism, such as glucoamylase, maltose permease, maltase, sugar transporters and maltose O-acetyltransferase (EC 2.3.1.79, which acetylates oligosaccharides). In the yeast S. cerevisiae, regulation of maltose utilization occurs by the MAL regulon (Chow et al, 1989) via the transcription activator (MALR), which induces maltose permease (MALT) and maltase (MALS) gene expression. Interestingly, among the 16 genes with significantly higher expression on maltose, we found genes encoding maltase in A. oryzae (AO090103000129 and AO090038000234), which correspond to orthologous genes of MALS in S. cerevisiae (see Fig.…”