Molecular Biology

Manufacturing snRNPs

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Science  15 Mar 2002:
Vol. 295, Issue 5562, pp. 1977
DOI: 10.1126/science.295.5562.1977b

Spinal muscular atrophy is a genetic disease in which motor neurons in the spinal cord degenerate. The protein encoded by this gene is called survival of motor neurons (SMN) and is one component of the large multiprotein SMN complex. Diverse cellular processes rely on RNA-protein assemblies, and the SMN complex is involved in the orderly construction of the small nuclear ribonucleoprotein particles (snRNPs) involved in pre-messenger RNA splicing.

Yong et al. show that the SMN complex recognizes one of the four stem loops (SL1) of the U1 snRNA and that this region is necessary and sufficient for SMN complex interaction. A distinct region is responsible for gathering the Sm proteins, which form a heteroheptameric ring encircling the snRNA; together they comprise the core of the U1 snRNP. Some Sm proteins contain an Arg-Gly motif, and a separate complex, called the methylosome, uses the protein methyltransferase PRMT5 to N-methylate the arginine symmetrically, as shown by Freisen et al. and Meister et al. The resulting dimethylarginine is recognized by SMN, facilitating the supply of Sm proteins to the SMN complex. — GJC

EMBO J.21, 1188 (2002); Mol. Cell. Biol.21, 8289 (2001); Curr. Biol.11, 1990 (2001).

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