The catalytic subunits of DNA polymerase delta of Schizosaccharomyces pombe and Saccharomyces cerevisiae share over 50% identity. The capability of S. pombe DNA polymerase delta to complement two thermosensitive mutants of S. cerevisiae was studied in vivo and it was determined that complementation was allele dependent. However, DNA polymerase delta from S. pombe did not restore growth of a S. cerevisiae strain containing a disrupted chromosomal copy of the POL3 gene that encodes DNA polymerase delta. To identify the regions of DNA polymerase delta responsible for species-specific interactions, we constructed different chimeras with S. cerevisiae and S. pombe DNA polymerase delta genes. The growth of a S. cerevisiae strain with a disrupted chromosomal POL3 gene was studied after transformation with plasmids expressing different chimeras. A 1254-bp region located in the 3' region of the S. cerevisiae POL3 gene is responsible for species-specific functions.