Regulatory evolution in proteins by turnover and lineage-specific changes of cyclin-dependent kinase consensus sites.

Evolutionary change in gene regulation is a key mechanism underlying the genetic component of organismal diversity. Here, we study evolution of regulation at the posttranslational level by examining the evolution of cyclin-dependent kinase (CDK) consensus phosphorylation sites in the protein subunits of the pre-replicative complex (RC). The pre-RC, an assembly of proteins formed during an early stage of DNA replication, is believed to be regulated by CDKs throughout the animals and fungi. Interestingly, although orthologous pre-RC components often contain clusters of CDK consensus sites, the positions and numbers of sites do not seem conserved. By analyzing protein sequences from both distantly and closely related species, we confirm that consensus sites can turn over rapidly even when the local cluster of sites is preserved, consistent with the notion that precise positioning of phosphorylation events is not required for regulation. We also identify evolutionary changes in the clusters of sites and further examine one replication protein, Mcm3, where a cluster of consensus sites near a nucleocytoplasmic transport signal is confined to a specific lineage. We show that the presence or absence of the cluster of sites in different species is associated with differential regulation of the transport signal. These findings suggest that the CDK regulation of MCM nuclear localization was acquired in the lineage leading to Saccharomyces cerevisiae after the divergence with Candida albicans. Our results begin to explore the dynamics of regulatory evolution at the posttranslational level and show interesting similarities to recent observations of regulatory evolution at the level of transcription.