Subtelomeric Regions Promote Evolutionary Innovation of Gene Families in Yeast

Abstract

Subtelomeres, the regions proximal to telomeres, are extremely dynamic parts of eukaryotic genomes. Gene families that reside in subtelomeres differ profoundly from non-subtelomeric gene families: they show increased recombination and duplication rates and often reflect the lifestyle of the organism under study. In the baker’s yeast Saccharomyces cerevisiae, subtelomeric gene families can be classified into three broad categories: genes involved in the utilization of alternative substrates, adhesion genes, and lastly, poorly characterized genes. Although the mechanisms shaping these gene families are not yet completely unraveled, studies on two typical subtelomeric gene families exemplify how the dynamic nature of chromosome ends can be exploited to rapidly evolve and diversify. Gene duplication has driven the evolution of the MAL gene families and provided closely related yeast species with appropriate, environment-specific alleles to metabolize various disaccharides. A second subtelomeric gene family, the adhesion (FLO) genes, shows frequent intergenic recombination between different FLO copies, thereby creating new FLO alleles with distinct adhesive properties. Moreover, stochastic transcriptional silencing and desilencing of subtelomeric genes could allow cells to ‘test’ these newly evolved genes without committing all cells in a population to the same fate.