Meta-Biol

• Pathways

Small nuclear ribonucleoproteins (snRNPs) are crucial for pre-mRNA processing to mRNAs. Each snRNP contains a small nuclear RNA (snRNA) and an extremely stable core of seven Sm proteins. The U6 snRNA differs from the other snRNAs; it binds seven Sm-like proteins and its assembly does not involve a cytoplasmic phase. The snRNP biogenesis pathway for all of the other snRNAs is complex, involving nuclear export of snRNA, Sm-core assembly in the cytoplasm and re-import of the mature snRNP. The assembly of the snRNA:Sm-core is carried out by the survival of motor neurons (SMN) complex. The SMN complex stringently scrutinizes RNAs for specific features that define them as snRNAs and binds the RNA-binding Sm proteins.

The term non-coding is commonly employed for RNA that does not encode a protein, but this does not mean that such RNAs do not contain information nor have function. There is considerable evidence that the majority of mammalian and other complex organism's genomes is transcribed into non-coding RNAs, many of which are alternatively spliced and/or processed into smaller products. Around 98% of all transcriptional output in humans is non-coding RNA. RNA-mediated gene regulation is widespread in higher eukaryotes and complex genetic phenomena like RNA interference are mediated by such RNAs. These non-coding RNAs are a growing list and include rRNAs, tRNAs, snRNAs, snoRNAs siRNAs, 7SL RNA, 7SK RNA, the RNA component of RNase P RNA, the RNA component of RNase MRP, and the RNA component of telomerase.

This superpathway encompasses the processes by which RNA transcription products are further modified covalently and non-covalently to yield their mature forms, and the regulation of these processes. Annotated pathways include ones for capping, splicing, and 3'-cleavage and polyadenylation to yield mature mRNA molecules that are exported from the nucleus (Hocine et al. 2010). mRNA editing and nonsense-mediated decay are also annotated. Processes leading to mRNA breakdown are described: deadenylation-dependent mRNA decay, microRNA-mediated RNA cleavage, and regulation of mRNA stability by proteins that bind AU-rich elements.psnRNP assembly is also annotated here.

The aminoacylation of mature tRNAs is annotated in the "Metabolism of proteins" superpathway, as a part of "Translation".