RNA recognition motif 1 (RRM1) found in vertebrate ribonucleoprotein PTB-binding 2 (raver-2)
This subgroup corresponds to the RRM1 of raver-2, a novel member of the heterogeneous nuclear ribonucleoprotein (hnRNP) family. It is present in vertebrates and shows high sequence homology to raver-1, a ubiquitously expressed co-repressor of the nucleoplasmic splicing repressor polypyrimidine tract-binding protein (PTB)-directed splicing of select mRNAs. In contrast, raver-2 exerts a distinct spatio-temporal expression pattern during embryogenesis and is mainly limited to differentiated neurons and glia cells. Although it displays nucleo-cytoplasmic shuttling in heterokaryons, raver2 localizes to the nucleus in glia cells and neurons. Raver-2 can interact with PTB and may participate in PTB-mediated RNA-processing. However, there is no evidence indicating that raver-2 can bind to cytoplasmic proteins. Raver-2 contains three N-terminal RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains), two putative nuclear localization signals (NLS) at the N- and C-termini, a central leucine-rich region, and a C-terminal region harboring two [SG][IL]LGxxP motifs. Raver-2 binds to PTB through the SLLGEPP motif only, and binds to RNA through its RRMs.