RNA recognition motif 2 (RRM2) found in heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) and similar proteins
This subgroup corresponds to the RRM2 of hnRNP A1, also termed helix-destabilizing protein, or single-strand RNA-binding protein, or hnRNP core protein A1, an abundant eukaryotic nuclear RNA-binding protein that may modulate splice site selection in pre-mRNA splicing. hnRNP A1 has been characterized as a splicing silencer, often acting in opposition to an activating hnRNP H. It silences exons when bound to exonic elements in the alternatively spliced transcripts of c-src, HIV, GRIN1, and beta-tropomyosin. hnRNP A1 can shuttle between the nucleus and the cytoplasm. Thus, it may be involved in transport of cellular RNAs, including the packaging of pre-mRNA into hnRNP particles and transport of poly A+ mRNA from the nucleus to the cytoplasm. The cytoplasmic hnRNP A1 has high affinity with AU-rich elements, whereas the nuclear hnRNP A1 has high affinity with a polypyrimidine stretch bordered by AG at the 3' ends of introns. hnRNP A1 is also involved in the replication of an RNA virus, such as mouse hepatitis virus (MHV), through an interaction with the transcription-regulatory region of viral RNA. Moreover, hnRNP A1, together with the scaffold protein septin 6, serves as host proteins to form a complex with NS5b and viral RNA, and further play important roles in the replication of Hepatitis C virus (HCV). hnRNP A1 contains two RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains), followed by a long glycine-rich region at the C-terminus. The RRMs of hnRNP A1 play an important role in silencing the exon and the glycine-rich domain is responsible for protein-protein interactions.