Protein-coding changes preceded cis-regulatory gains in a newly evolved transcription circuit

Abstract

Generating a new transcriptional network Organismal novelties result from changes in transcriptional circuits. But what comes first, changes in regulatory protein or changes in cis-regulatory sequences? Britton et al. examine the Matα2 protein in a Saccharomycotina clade of fungi. They show that a newly evolved transcription circuit involving repression of the a-specific genes by the ancient homeodomain protein Matα2 occurred in two stages separated by millions of years. In the first stage, Matα2 acquired several coding changes followed by changes in cis-regulatory sequences. This clade-specific requirement explains how the coding changes of Matα2 were in place long before the new a-specific gene repression circuit arose. Science , this issue p. 96