The DNA replication protein Orc1 from the yeast Torulaspora delbrueckii is required for heterochromatin formation but not as a silencer-binding protein.

To understand the process by which new protein functions emerge, we examined how the yeast heterochromatin protein Sir3 arose through gene duplication from the conserved DNA replication protein Orc1. Orc1 is a subunit of the origin recognition complex (ORC), which marks origins of DNA replication. In Saccharomyces cerevisiae, Orc1 also promotes heterochromatin assembly by recruiting the structural proteins Sir1-4 to silencer DNA.

Conservation of a DNA Replication Motif among Phylogenetically Distant Budding Yeast Species.

Eukaryotic DNA replication begins at genomic loci termed origins, which are bound by the origin recognition complex (ORC). Although ORC is conserved across species, the sequence composition of origins is more varied. In the budding yeast Saccharomyces cerevisiae, the ORC-binding motif consists of an A/T-rich 17 bp "extended ACS" sequence adjacent to a B1 element composed of two 3-bp motifs.

Evolution of Distinct Responses to Low NAD Stress by Rewiring the Sir2 Deacetylase Network in Yeasts.

Evolutionary adaptation increases the fitness of a species in its environment. It can occur through rewiring of gene regulatory networks, such that an organism responds appropriately to environmental changes. We investigated whether sirtuin deacetylases, which repress transcription and require NAD for activity, serve as transcriptional rewiring points that facilitate the evolution of potentially adaptive traits.