RNA recognition motif 1 (RRM1) found in vertebrate ribonucleoprotein PTB-binding 1 (raver-1)
This subgroup corresponds to the RRM1 of raver-1, a ubiquitously expressed heterogeneous nuclear ribonucleoprotein (hnRNP) that serves as a co-repressor of the nucleoplasmic splicing repressor polypyrimidine tract-binding protein (PTB)-directed splicing of select mRNAs. It shuttles between the cytoplasm and the nucleus and can accumulate in the perinucleolar compartment, a dynamic nuclear substructure that harbors PTB. Raver-1 also modulates focal adhesion assembly by binding to the cytoskeletal proteins, including alpha-actinin, vinculin, and metavinculin (an alternatively spliced isoform of vinculin) at adhesion complexes, particularly in differentiated muscle tissue. Raver-1 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 PTB-binding [SG][IL]LGxxP motifs. Raver1 binds to PTB through the PTB-binding motifs at its C-terminal half, and binds to other partners, such as RNA having the sequence UCAUGCAGUCUG, through its N-terminal RRMs. Interestingly, the 12-nucleotide RNA having the sequence UCAUGCAGUCUG with micromolar affinity is found in vinculin mRNA. Additional research indicates that the RRM1 of raver-1 directs its interaction with the tail domain of activated vinculin. Then the raver1/vinculin tail (Vt) complex binds to vinculin mRNA, which is permissive for vinculin binding to F-actin.