RING finger found in polycomb group RING finger protein 6 (PCGF6) and similar proteins
PCGF6, also known as Mel18 and Bmi1-like RING finger (MBLR), or RING finger protein 134 (RNF134), is one of six PcG RING finger (PCGF) homologs (PCGF1/NSPc1, PCGF2/Mel-18, PCGF3, PCGF4/BMI1, PCGF5, and PCGF6/MBLR) and serves as the core component of a noncanonical Polycomb repressive complex 1 (PRC1)-like L3MBTL2 complex, which is composed of some canonical components, such as RNF2, CBX3, CXB4, CXB6, CXB7, and CXB8, as well as some noncanonical components, such as L3MBTL2, E2F6, WDR5, HDAC1, and RYBP, and plays a critical role in epigenetic transcriptional silencing in higher eukaryotes. Like other PCGF homologs, PCGF6 possesses the transcriptional repression activity, and also associates with ring finger protein 2 (RNF2) to form a RNF2-PCGF heterodimer, which is catalytically competent as an E3 ubiquitin transferase and is the scaffold for the assembly of additional components. Moreover, PCGF6 can regulate the enzymatic activity of JARID1d/KDM5D, a trimethyl H3K4 demethylase, through the direct interaction with it. Furthermore, PCGF6 is expressed predominantly in meiotic and post-meiotic male germ cells and may play important roles in mammalian male germ cell development. It also regulates mesodermal lineage differentiation in mammalian embryonic stem cells (ESCs) and functions in induced pluripotent stem (iPS) reprogramming. The activity of PCGF6 is found to be regulated by cell cycle dependent phosphorylation. PCGF6 contains a C3HC4-type RING-HC finger.