NOVEL STRUCTURAL FEATURES OF BOVINE PAPILLOMAVIRUS CAPSID REVEALED BYA 3-DIMENSIONAL RECONSTRUCTION TO 9-ANGSTROM RESOLUTION

The three-dimensional structure of bovine papillomavirus has been dete rmined to 9 Angstrom resolution by reconstruction of high resolution, low dose cryo-electron micrographs of quench-frozen virions. Although hexavalent and pentavalent capsomeres form star-shaped pentamers of th e major capsid protein L1, they have distinct high-resolution structur es. Most prominently, a 25 Angstrom hole in the centre of hexavalent c apsomeres is occluded in the pentavalent capsomeres. This raises the p ossibility that the 1.2 minor capsid protein is located in the centre of the pentavalent capsomeres. Intercapsomere connections similar to 1 0 Angstrom in diameter were clearly resolved. These link adjacent caps omeres and are reminiscent of the helical connections that stabilize p olyomavirus.