The PRI1 gene of Saccharomyces cerevisiae encodes for the p48 polypeptide of DNA primase. We have determined the nucleotide sequence of a 1,965 bp DNA fragment containing the PRI1 locus. The entire coding sequence of the gene lies within an open reading frame, and there are 409 amino acids in the single polypeptide protein if translation is assumed to start at the first ATG in this frame. The 5' and 3' end-points of PRI1 mRNA have been determined by S1 mapping and primer extension analysis. The primary structure and the codon usage of PRI1 suggest that this essential gene is poorly expressed in yeast cells.