Fig. 1. Impact of snf mutations on snRNP assembly. (A) Schematic representation of SNF, the Drosophila U1A/U2B'' protein. SNF contains two RRM domains (for RNA recognition motif) separated by a short linker region. The arrows indicate the location of the mutations used in this study. As indicated, the sequence of the N- and C-terminal RRM motifs share significant sequence identity with both the human U1A and U2B'' proteins. (B) Amino acid sequence alignment of the N-terminal RRM domain from SNF and the human U1A and U2B'' proteins and the amino acid substitutions associated with each snf allele used. Identical amino acids are indicated by black dots above the sequence. (C) snRNP incorporation was tested by immunoprecipitation of SNF from extracts made from adult flies of the indicated genotype followed by northern blotting to detect U1 and U2 snRNAs in RNA extracted from the precipitated fractions.