Publisher Summary The snRNAs exist in the cell as ribonucleoprotein (RNP) complexes. While the snRNAs U1, U2, and U5 are organized in separate RNP particles, the majority of the snRNAs U4 and U6 reside in a single RNP complex. Several proteins in the molecular weight range of 25K to 200K were recently identified as possible U5-specific proteins. Information about the primary structure of the U I- and U2-specific proteins as well as the common snRNP proteins E and D has recently been obtained by cDNA cloning. The combined use of the antibody systems with DEAE ion-exchange chromatography allows fractionation of individual snRNP types. As an alternative, the mixture of snRNPs purified by anti-m3G or anti-m6A affinity columns may be fractionated by ion-exchange chromatography on Mono-Q columns under FPLC conditions. The availability of such protein-deficient snRNP populations is expected to be of substantial value for the investigation of the roles of individual snRNP proteins in the functioning of the snRNPs during splicing.