Spliceosomes and Snurposomes

In cell extracts, the snRNAs exist associated with proteins as small nuclear ribonucleoproteins (snRNPs, pronounced «snurps»). In an in vitro splicing reaction, the snRNPs, other essential protein factors, and the pre-mRNA form a macromolecular complex known as a spliceosome. Spliceosomes can be isolated from the reaction in relatively pure form for biochemical studies; in the electron microscope they appear as 40- to 60-nm particles with a distinctive morphology. Much of our knowledge comes from in vitro biochemical experiments