RNA recognition motif 3 (RRM3) found in heterogeneous nuclear ribonucleoprotein hnRNP H , hnRNP H2, hnRNP F and similar proteins
This subgroup corresponds to the RRM3 of hnRNP H (also termed mcs94-1), hnRNP H2 (also termed FTP-3 or hnRNP H') and hnRNP F, which represent a group of nuclear RNA binding proteins that play important roles in the regulation of alternative splicing decisions. hnRNP H and hnRNP F are two closely related proteins, both of which bind to the RNA sequence DGGGD. They are present in a complex with the tissue-specific splicing factor Fox2, and regulate the alternative splicing of the fibroblast growth factor receptor 2 (FGFR2) transcripts. The presence of Fox 2 can allows hnRNP H and hnRNP F to better compete with the SR protein ASF/SF2 for binding to FGFR2 exon IIIc. Thus, hnRNP H and hnRNP F can function as potent silencers of FGFR2 exon IIIc inclusion through an interaction with the exonic GGG motifs. Furthermore, hnRNP H and hnRNP H2 are almost identical; bothe have been found to bind nuclear-matrix proteins. hnRNP H activates exon inclusion by binding G-rich intronic elements downstream of the 5' splice site in the transcripts of c-src, human immunodeficiency virus type 1 (HIV-1), Bcl-X, GRIN1, and myelin. It silences exons when bound to exonic elements in the transcripts of beta-tropomyosin, HIV-1, and alpha-tropomyosin. hnRNP H2 has been implicated in pre-mRNA 3' end formation. Members in this family contain three RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains). RRM1 and RRM2 are responsible for the binding to the RNA at DGGGD motifs, and they play an important role in efficiently silencing the exon. In addition, the family members have an extensive glycine-rich region near the C-terminus, which may allow them to homo- or heterodimerize.