The telomere-associated MAL3 locus of Saccharomyces is a tandem array of repeated genes

Saccharomyces strains capable of fermenting maltose contain any one of five telomere-associated MAL loci. Each MAL locus is a complex of three genes encoding the three functions required to ferment maltos: maltose permease (GENE 1), maltase (GENE 2) and the MAL trans-activator (GENE 3). All five loci have been cloned and all are highly sequence homologous over least a 9-0 kbp region containing these GENEs (Charron et al., Genetics122, 307–331, 1989). Our initial studies of strians carrying the MAL3 locus indicated the presence of linked, repeated MLA-homologous sequences (Michels and Needleman, Mol. Gen. Genet.191, 225–230, 1983). Here we report our analysis of the centromere-proximal MAL3-linked sequence and show that the complete MAL3 locus spans approximately 40 kbp and consists of tandemly arrayed, partial repeats of the three GENE sequences described above. In addition, the structure of the MAL3 locus is compared to that of three partially functional alleles of MAL3. These alleles were shown to contain only MAL31 and MAL32 and their structure suggests that they resulted from MAL3 deletions removing the sequences centromere-proximal of MAL31. The amplification and rerrangement of the telomer-linked MAL3 sequences are discussed in the context of studies on other telemere-associated sequences from yeast and other species.