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Abstract

Virtually, all eukaryotic mRNAs are synthesized as precursor molecules that need to be extensively processed in order to serve as a blueprint for proteins. The three most prevalent processing steps are the capping reaction at the 5′‐end, the removal of intervening sequences by splicing, and the formation of poly (A)‐tails at the 3′‐end of the message by polyadenylation. A large number of proteins and small nuclear ribonucleoprotein complexes (snRNPs) interact with the mRNA and enable the different maturation steps. This chapter focuses on the biogenesis of snRNPs, the major components of the pre‐mRNA splicing machinery (spliceosome). A large body of evidence has revealed an intricate and segmented pathway for the formation of snRNPs that involves nucleo‐cytoplasmic transport events and elaborates assembly strategies. We summarize the knowledge about the different steps with an emphasis on trans‐acting factors of snRNP maturation of higher eukaryotes. WIREs RNA 2011 2 718–731 DOI: 10.1002/wrna.87