Small nuclear ribonucleoprotein
ID: small-nuclear-ribonucleoprotein
A small nuclear ribonucleoprotein is a ribonucleoprotein particle containing a small nuclear RNA assembled with proteins. Several such particles cooperate in the spliceosome, which removes introns from precursor messenger RNA. U1 snRNP is a concrete example: its U1 small nuclear RNA helps recognize a splice donor site, while its proteins stabilize and organize the particle.[ref]
Crystal structure of human spliceosomal U1 snRNP at 5.5 Å resolution by Daniel A. Pomeranz Krummel and others. Introduction, spliceosomal particles and U1 composition
The distinction between component and assembly matters. An isolated small nuclear RNA is not the entire small nuclear ribonucleoprotein. Human U1 contains an RNA and ten proteins, including seven different Sm proteins. Nor is one U1 particle by itself the complete spliceosome.[ref]
Crystal structure of human spliceosomal U1 snRNP at 5.5 Å resolution by Daniel A. Pomeranz Krummel and others. Abstract and Introduction, U1 RNA, seven Sm proteins and three U1-specific proteins
A structural experiment rebuilt a functional U1 core from separately prepared components and determined a X-ray crystallography map. Labels containing heavy atoms helped identify which protein occupied which density. The crystallized particle was engineered and lacked one native U1 protein; modeling a complete particle required additional structural information.[ref]
Crystal structure of human spliceosomal U1 snRNP at 5.5 Å resolution by Daniel A. Pomeranz Krummel and others. Structure determination, Figures1–4 and model in Figure5
For an original completeness example, detecting an RNA together with one of its expected proteins establishes co-recovery of those components. It does not establish that all ten proteins occupy each recovered particle. Comparing component inventories with a functional RNA splicing assay tests composition and activity separately.
New to topics? Read the docs here!