Removal of introns from pre-messenger RNA (pre-mRNA) requires small nu
clear RNAs (snRNAs) packaged into stable small ribonucleoprotein parti
cles (snRNP). These snRNPs contain specific and common proteins also c
alled Sm proteins. Correct assembly of the snRNAs with the common prot
eins is an essential step for the biogenesis of snRNP particles. We ha
ve identified a new Saccharomyces serevisiae gene, SME1 whose product
shows 45% identity with the E core protein of human snRNP. The Sme1p c
ontains the evolutionary conserved residues found in all Sm proteins.
Combining genetic and biochemical experiments, we show that SME1 is an
essential gene required for pre-mRNA splicing, cap modification and U
1, U2, U4 and U5 snRNA stability. We show also that the human E core p
rotein complements a yeast SME1 disruption demonstrating the functiona
l equivalence of Sme1p and the human E core protein.