The DNA sequence of an open reading frame (ORF) corresponding to the canine adenovirus type 1 (Can1) proteinase gene was determined. A total of 1171 base pairs were sequenced from the downstream end of the HindIII-A Can1 genomic fragment, including adjacent regions corresponding to the carboxy-terminal portions of the hexon and the DNA-binding proteins. The predicted Can1 proteinase consists of 206 residues (23,325 D) of which 68% are identical and 83% are similar to the sequence of the human Ad2 proteinase. Alignment with the Ad2 proteinase identified a number of conserved residues that could form part of the catalytic triad of the enzyme.