Characterization of the gene encoding the A-type inclusion body protein of mousepox virus.

The gene of the mousepox virus strain MP-1 coding for the protein of A-type inclusions was identified and sequenced. The gene maps in the HindIII-A fragment at the same position as the cowpox-virus Brighton 160 kD gene (1) and the closely related 94 kD LS gene of vaccinia virus strain Western Reserve (2,3). The encoded protein consists of 1049 amino acids with a predicted molecular weight of 122.5 kD, which corresponds well to the apparent molecular weight of 130 kD estimated after polyacrylamide gel electrophoresis and Western blotting. The protein is a characteristic feature of mousepox virus and could be demonstrated for five independently isolated strains. The MP-1 ATI protein displays a similarity of 82.3% to the cowpox virus Brighton 160 kD protein, the first 340 amino acids being almost identical. However, two major deletions of 55 and 92 amino acids were observed from amino acid positions 671 to 732 and 794 to 885, respectively. Furthermore, the C-terminal residues (position 998-1049 of the MP-1 sequence) did not match at satisfactory levels with cowpox nor with vaccinia virus sequences. According to Western blot and protein alignment data as well as hydropathy predictions, the 130 and 160 kD proteins closely resemble each other, indicating similar structure and function.