Small Nuclear Ribonucleoproteins (sn RNP s)

Abstract

Abstract Small nuclear ribonucleoproteins (snRNPs) are protein– ribonucleic acid (RNA) complexes defined by a core noncoding RNA of approximately 100–600 nucleotides and tightly bound proteins that together accumulate in the nucleus. The snRNPs are best known for their role in RNA splicing complexes, including U1, U2, U4, U5 and U6 snRNPs found in the spliceosome. Additional snRNPs are functionally diverse, but in many cases the RNA component of snRNPs can base‐pair with a substrate for precise alignment and possible catalysis. The U7 snRNP directs 3′‐end mRNA formation for histone transcripts, and the 7SK snRNP regulates transcription. Two special groups of snRNPs, small nucleolar RNPs (snoRNPs) and small Cajal‐body RNPs (scaRNPs) , are restricted to their named subnuclear compartments in order to direct post‐transcriptional modification of ribosomal and splicing RNAs, respectively. Certain herpesviruses express high levels of novel snRNPs involved in the regulation of gene expression. Due to their important biological roles, there are many diseases associated with snRNPs. Key Concepts: The snRNPs are small nuclear ribonucleoprotein particles, a class of dynamic RNA–protein complexes that accumulate in the nucleus. Major and minor splicing snRNPs form super‐complexes (spliceosomes) that direct the precise splicing of messenger RNAs. In the special process of trans ‐splicing, splice leader (SL) snRNPs donate RNA to the ends of transcripts. The U7 snRNP coordinates 3′ end processing of metazoan histone messenger RNAs. The 7SK snRNP regulates transcription by selectively sequestering and rendering inactive the P‐TEFb protein, a key modulator of RNA polymerase II. Two groups of snRNPs are singled out for specific subnuclear localisation: small nucleolar and small Cajal‐body associated (sno/scaRNPs) direct methylation and pseudouridylation of splicing and ribosomal RNAs. Some mammalian herpesviruses express viral snRNPs, which have enigmatic and complex functions in gene regulation. Several diseases including lupus present autoantibody production of antibodies directed at snRNP‐affiliated proteins such as Sm, Lsm and La. Most snRNPs have been affiliated with diseases and are therefore promising biomarkers for diagnosis and prognosis.