RNA recognition motif 1 (RRM1) found in vertebrate RNA binding motif protein 15 (RBM15)
This subgroup corresponds to the RRM1 of RBM15, also termed one-twenty two protein 1 (OTT1), conserved in eukaryotes, a novel mRNA export factor and component of the NXF1 pathway. It binds to NXF1 and serves as receptor for the RNA export element RTE. It also possesses mRNA export activity and can facilitate the access of DEAD-box protein DBP5 to mRNA at the nuclear pore complex (NPC). RBM15 belongs to the Spen (split end) protein family, which contains three N-terminal RNA recognition motifs (RRMs), also known as RBD (RNA binding domain) or RNP (ribonucleoprotein domain), and a C-terminal SPOC (Spen paralog and ortholog C-terminal) domain. This family also includes a RBM15-MKL1 (OTT-MAL) fusion protein that RBM15 is N-terminally fused to megakaryoblastic leukemia 1 protein (MKL1) at the C-terminus in a translocation involving chromosome 1 and 22, resulting in acute megakaryoblastic leukemia. The fusion protein could interact with the mRNA export machinery. Although it maintains the specific transactivator function of MKL1, the fusion protein cannot activate RTE-mediated mRNA expression and has lost the post-transcriptional activator function of RBM15. However, it has transdominant suppressor function contributing to its oncogenic properties.