Natural selection on gene order in the genome reorganization process after whole-genome duplication of yeast

A genome must locate its coding genes on the chromosomes in a meaningful manner with the help of natural selection, but the mechanism of gene order evolution is poorly understood. To explore the role of selection in shaping the current order of coding genes and their cis-regulatory elements, a comparative genomic approach was applied to the baker's yeast Saccharomyces cerevisiae and its close relatives. S. cerevisiae have experienced a whole-genome duplication followed by an extensive reorganization process of gene order, during which a number of new adjacent gene pairs appeared. We found that the proportion of new adjacent gene pairs in divergent orientation is significantly reduced, suggesting that such new divergent gene pairs may be disfavored most likely because their coregulation may be deleterious. It is also found that such new divergent gene pairs have particularly long intergenic regions. These observations suggest that selection specifically worked against deletions in intergenic regions of new divergent gene pairs, perhaps because they should be physically kept away so that they are not coregulated. It is indicated that gene regulation would be one of the major factors to determine the order of coding genes.