As an initial step towards the characterization of replicative DNA polymerases of trypanosomes, we have cloned, sequenced and examined the expression of the Trypanosoma (Trypanozoon) brucei brucei gene that encodes the DNA polymerase α catalytic core (polα). The protein sequence contains the six conserved regions that have been recognized previously in eukaryotic and viral replicative DNA polymerases. In addition, we have identified a seventh region which appears to be conserved primarily in α-type DNA polymerases. The T.brucei DNA pol α core N-terminus is 123 and 129 amino acids smaller than that of the human and yeast homologue, respectively. The gene is separated by 386 bp from an upstream open reading frame (ORF) of 442 codons. Stable transcripts of the upstream sequence are detected in both dividing and non-dividing forms, while polα transcripts are detected principally in dividing forms. Allelic copies of the T.brucei polα region exhibit restriction site polymorphisms; one such sequence polymorphism affects the amino acid sequence of the T.brucei DNA polα core. The T.brucei polα region cross-hybridizes weakly with that of T.(Nannomonas) congolense and T.(Duttonella) vivax .