Deciphering the assembly pathway of Sm-class U snRNPs

Abstract 

The assembly of the Sm-class of uridine-rich small nuclear ribonucleoproteins (U snRNPs), albeit spontaneous in vitro, has recently been shown to be dependent on the aid of a large number of assisting factors in vivo. These factors are organized in two interacting units termed survival motor neuron (SMN)- and protein arginine methyltransferase 5 (PRMT5)-complexes, respectively. While the PRMT5-complex acts early in the assembly pathway by activating common proteins of U snRNPs, the SMN-complex functions to join proteins and RNA in a highly ordered, apparently regulated manner. Here, we summarize recent progress in the understanding of this process and discuss the influence exerted by the aforementioned trans-acting factors.

Abbreviations: snRNA, small nuclear RNA, snRNP, small nuclear ribonucleoprotein, SMN, survival motor neuron, PRMT5, protein arginine methyltransferase 5, WD45, WD repeat domain 45, pICln, chloride conductance regulatory protein, CBC, cap-binding complex, PHAX, phosphorylated adaptor for RNA export, CRM1, chromosome region maintenance 1, RanGTP, Ras-related nuclear protein bound to GTP, NPC, nuclear pore complex, Tgs1, trimethylguanosine synthetase1, NLS, nuclear localization signal, SPN1, snurportin-1, Lsm proteins, like Sm protein

Keywords: U snRNP biogenesis, SMN-complex, PRMT5-complex, Sm proteins, Splicing, U snRNA