12 The Ever-Growing World of Small Nuclear Ribonucleoproteins

Small null r ibo n ucleo p roteins (RNPs)—defined as tight complexes of one or more proteins with a short RNA molecule (usually 60–300 nucleotides)—inhabit every compartment of eukaryotic cells. Those that reside in the nucleus, the null s mall null n uclear null RNPs null (snRNPs), can themselves be divided into two families. There are snRNPs of the nucleoplasm, whose major business is the generation of messenger RNAs for export to the...