Energy costs constrain the evolution of gene expression.

Changes in gene expression affect the energy budget of a cell. A previous contribution estimated the energetic cost of yeast mRNA and protein expression from very limited information on protein half-lives. Using recently published genome-scale measurements of protein half-lives, I here confirm that even small increases in gene expression are opposed by natural selection. In small organisms with large effective population sizes, the evolution of transcription and translation rates are thus not evolutionarily neutral processes. (c) 2007 Wiley-Liss, Inc.