RNA recognition motif 3 (RRM3) found in vertebrate polypyrimidine tract-binding protein 2 (PTBP2)
This subgroup corresponds to the RRM3 of PTBP2, also known as neural polypyrimidine tract-binding protein or neurally-enriched homolog of PTB (nPTB), highly homologous to polypyrimidine tract binding protein (PTB) and perhaps specific to the vertebrates. Unlike PTB, PTBP2 is enriched in the brain and in some neural cell lines. It binds more stably to the downstream control sequence (DCS) RNA than PTB does but is a weaker repressor of splicing in vitro. PTBP2 also greatly enhances the binding of two other proteins, heterogeneous nuclear ribonucleoprotein (hnRNP) H and KH-type splicing-regulatory protein (KSRP), to the DCS RNA. The binding properties of PTBP2 and its reduced inhibitory activity on splicing imply roles in controlling the assembly of other splicing-regulatory proteins. PTBP2 contains four RNA recognition motifs (RRMs), also known as RBD (RNA binding domain) or RNP (ribonucleoprotein domain).