Characterization of the putative maltose transporters encoded by YDL247w and YJR160c.

The maltose permease family of Saccharomyces cerevisiae comprises five proteins, three of which are characterized, MAL31, MAL61 and AGT1 and two putative permeases, YDL247w (MPH2) and YJR160c (MPH3). The two uncharacterized permeases share 100% identity and have 75% identity with MAL31 and MAL61 and 55% identity with AGT1. Characterization of the genes YDL247w and YJR160c confirmed that they encode alpha-glucoside permeases capable of transporting maltose, maltotriose, alpha-methylglucoside and turanose. Analysis of the promoter regions identified regulatory elements, binding sites for the transcriptional activator, Malx3p and the inhibitory protein, Mig1p. Further analysis of the flanking sequences located blocks of identity covering five open reading frames, indicating that this region was involved in chromosomal block duplication. The members of the maltose permease family are proteins that have strongly overlapping but nevertheless distinct functions, which is a selective advantage for yeast, as it reflects successful adaptation to the variety of environmental conditions to which the yeast cells are exposed; such adaptability is very important in an industrial context. Copyright 2002 John Wiley & Sons, Ltd.