This family of proteins is conserved from fungi to human. In yeasts it is involved in the ubiquitination of histones H2A and H2B. This ubiquitination step is a vital one in the regulation of the transcriptional activity of RNA polymerase II. In S. cerevisiae, Rad6 and Bre1 are present in a complex, also containing Lge1, that is required for H2B ubiquitination. Bre1 is the H2B ubiquitin ligase that interacts with acidic activators, such as Gal4, and recruits Rad6 and its binding partner Lge1 to target promoters. In S. pombe the equivalent protein to Lge1 appears to be Shf1. In human, periphilin acts a transcriptional co-repressor and regulates cell cycle progression.