The Saccharomyces cerevisiae SNP1 gene encodes a protein that shares 30% amino acid identity with the mammalian U1 small nuclear ribonucleoprotein particle protein 70K (U1-70K). We have demonstrated that yeast strains in which the SNP1 gene was disrupted are viable but exhibit greatly increased doubling times and severe temperature sensitivity. Furthermore, snp1-null strains are defective in pre-mRNA splicing. We have tested deletion alleles of SNP1 for their ability to complement these phenotypes. We found that the highly conserved RNA recognition motif consensus domain of Snp1 is not required for complementation of the snp1-null growth or splicing defects nor for the in vivo association with the U1 small nuclear ribonucleoprotein particle. However, the amino-terminal domain of Snp1, less strongly conserved, is necessary and sufficient for complementation.