FIG. 1.

Organization of UL26 and UL26.5. The numbers refer to the amino acid residues in UL26, and the small vertical arrows indicate the proteolytic cleavage sites. The primary product of the UL26 ORF is the full-length (635-amino-acid) protease. This undergoes self-cleavage at the release (R) and maturation (M) sites to generate the B_SC capsid proteins VP24 (247 amino acids) and VP21 (363 amino acids), respectively. The primary product of the UL26.5 ORF is the major scaffolding protein, pre-VP22a (328 amino acids), which is cleaved at the M site by the UL26 protease to generate the B_SC capsid protein VP22a (303 amino acids). The mutation in ts1201 maps to the VP24 portion of the protease (21).