Selection on the genic location of disruptive elements.

Analyses of nucleotide patterns in coding regions of prokaryotes have revealed that selection acts on DNA and RNA stability and on translational accuracy. Here we examine the positions of mononucleotide repeats within microbial genes and detect a pervasive bias in the locations of these disruptive elements that becomes more pronounced with increases in repeat length. We argue that, because these repeats are mutagenic, this pattern arose to minimize the costs associated with transcribing and translating nonfunctional genes, supporting a view that pseudogenes need not be evolving in a strictly neutral manner.