RTM1: a member of a new family of telomeric repeated genes in yeast.

We have isolated a new yeast gene called RTM1 whose overexpression confers resistance to the toxicity of molasses. The RTM1 gene encodes a hydrophobic 34-kD protein that contains seven potential transmembrane-spanning segments. Analysis of a series of industrial strains shows that the sequence is present in multiple copies and in variable locations in the genome. RTM loci are always physically associated with SUC telomeric loci. The SUC-RTM sequences are located between X and Y' subtelomeric sequences at chromosome ends. Surprisingly RTM sequences are not detected in the laboratory strain X2180. The lack of this sequence is associated with the absence of any SUC telomeric gene previously described. This observation raises the question of the origin of this nonessential gene. The particular subtelomeric position might explain the SUC-RTM sequence amplification observed in the genome of yeasts used in industrial biomass or ethanol production with molasses as substrate. This SUC-RTM sequence dispersion seems to be a good example of genomic rearrangement playing a role in evolution and environmental adaptation in these industrial yeasts.