RNA recognition motif (RRM) found in Saccharomyces cerevisiae protein Nrd1, Schizosaccharomyces pombe Rpb7-binding protein seb1 and similar proteins
This subfamily corresponds to the RRM of Nrd1 and Seb1. Nrd1 is a novel heterogeneous nuclear ribonucleoprotein (hnRNP)-like RNA-binding protein encoded by gene NRD1 (for nuclear pre-mRNA down-regulation) from yeast S. cerevisiae. It is implicated in 3' end formation of small nucleolar and small nuclear RNAs transcribed by polymerase II, and plays a critical role in pre-mRNA metabolism. Nrd1 contains an RNA recognition motif (RRM), also termed RBD (RNA binding domain) or RNP (ribonucleoprotein domain), a short arginine-, serine-, and glutamate-rich segment similar to the regions rich in RE and RS dipeptides (RE/RS domains) in many metazoan splicing factors, and a proline- and glutamine-rich C-terminal domain (P+Q domain) similar to domains found in several yeast hnRNPs. Disruption of NRD1 gene is lethal to yeast cells. Its N-terminal domain is sufficient for viability, which may facilitate interactions with RNA polymerase II where Nrd1 may function as an auxiliary factor. By contrast, the RRM, RE/RS domains, and P+Q domain are dispensable. Seb1 is an RNA-binding protein encoded by gene seb1 (for seven binding) from fission yeast S. pombe. It is essential for cell viability and bound directly to Rpb7 subunit of RNA polymerase II. Seb1 is involved in processing of polymerase II transcripts. It also contains one RRM motif and a region rich in arginine-serine dipeptides (RS domain).