The Saccharomyces cerevisiae SNP1 gene encodes the U1 snRNP specific protein U1-70K. The RRM and glycine rich domains are well conserved from yeast to metazoan U1-70K proteins, with over 80% amino acid similarity. We have demonstrated that yeast strains in which the SNP1 gene was disrupted were viable, but exhibited greatly increased doubling rates and severe temperature sensitivities. In addition snp1-null strains were defective in nuclear, pre-mRNA splicing. We have tested deletion alleles of SNP1 for their ability to complement these phenotypes. We found that the highly conserved RRM and glycine rich domains of Snp1 were not required for complementation of the snp1-null growth or splicing defects. However, the amino terminal domain of Snp1, which is not highly conserved, was necessary and sufficient for complementation.