Compositional constraints and genome evolution

Abstract
Nucleotide sequences of all genomes are subject to compositional constraints that (1) affect, to about the same extent, both coding and noncoding sequences; (2) influence not only the structure and function of the genome, but also those of transcripts and proteins; (3) are the result of environmental pressures; and (4) largely control the fixation of mutations. These findings indicate (1) that noncoding sequences are associated with biological functions; (2) that the organismal phenotype comprises two components, the classical phenotype, corresponding to the “gene products,” and a “genome phenotype,” which is defined by the compositional constraints; and (3) that natural selection plays a more important role in genome evolution than do random events.