3-DIMENSIONAL STRUCTURE OF VACCINIA VIRUS-PRODUCED HUMAN PAPILLOMAVIRUS TYPE-1 CAPSIDS

The capsid proteins of papillomavirus self-assemble to form empty caps ids or virus-like particles that appear quite similar to naturally occ urring virions by conventional electron microscopy. To characterize su ch virus-like particles more fully, cryoelectron microscopy and image analysis techniques were used to generate three dimensional reconstruc tions of capsids produced by vaccinia virus recombinants (V capsids) t hat expressed human papillomavirus type 1 L1 protein only or both L1 a nd L2 proteins. AH V capsids had 72 pentameric capsomers arranged on a T=7 icosahedral lattice. Each particle (similar to 60 nm in diameter) consisted of an similar to 2-nm-thick shell of protein with a radius of 22 nm with capsomers that extend similar to 6 nm from the shell. At a resolution of 3.5 nm, both V capsid structures appear identical to the capsid structure of native human papillomavirus type 1 (T. S. Bake r, W. W. Newcomb, N. H. Olson, L. M. Cowsert, C. Olson, and J. C. Brow n, Biophys. J. 60:1445-1456, 1991), thus implying that expressed and n ative capsids are structurally equivalent.