CONSERVED FEATURES IN PAPILLOMAVIRUS AND POLYOMAVIRUS CAPSIDS

Capsids of papilloma and polyoma viruses (papovavirus family) are comp osed of 72 pentameric capsomeres arranged on a skewed icosahedral latt ice (triangulation number of seven, T = 7). Cottontail rabbit papillom avirus (CRPV) was reported previously to be a T = 7laevo (left-handed) structure, whereas human wart virus, simian virus 40, and murine poly omavirus were shown to be T = 7dextro (right-handed). The CRPV structu re determined by cryoelectron microscopy and image reconstruction was similar to previously determined structures of bovine papillomavirus t ype 1 (BPV-1) and human papillomavirus type 1 (HPV-1). CRPV capsids we re observed in closed (compact) and open (swollen) forms. Both forms h ave star-shaped capsomeres, as do BPV-1 and HPV-1, but the open CRPV c apsids are similar to 2 nm larger in radius. The lattice hands of all papillomaviruses examined in this study were found to be T = 7dextro. In the region of maximum contact, papillomavirus capsomeres interact i n a manner similar to that found in polyomaviruses. Although papilloma and polyoma viruses have differences in capsid size (similar to 60 ve rsus similar to 50 nm), capsomere morphology (11 to 12 nm star-shaped versus 8 nm barrel-shaped), and intercapsomere interactions (slightly different contacts between capsomeres), papovavirus capsids have a con served, R-pentamer, T = 7dextro structure. These features are conserve d despite significant differences in amino acid sequences of the major capsid proteins. The conserved features may be a consequence of stabl e contacts that occur within capsomeres and flexible links that form a mong capsomeres. (C) 1996 Academic Press Limited