Conserved sequences and the evolution of gene regulatory signals.

Studies of evolutionary conservation of gene regulatory signals have led to a paradox: extensive sequence similarity implies functional conservation in non-coding regions across mammalian species; however, this stands in contrast to our understanding of transcriptional regulatory sites composed of degenerate recognition sequences for transcription factors that can maintain functional equivalence despite considerable sequence divergence. The latter observation provides an explanation for the rapid evolution of new traits through the gain and loss of transcription factor binding sites that bring new genes under the control of an existing genetic regulatory network. The former observation might point to novel mechanisms of gene regulation and/or chromosome function that are currently unappreciated. Recent comparative genome analysis has highlighted extensive conserved sequences in mammalian genomes that are beginning to be functionally characterized.