Structural Roles of Polyoma Virus Proteins

Abstract

The superhelical, closed circular form of polyoma deoxyribonucleic acid (DNA) (Co 1) is bound in a 25S DNA-protein complex to the viral histone-like proteins after alkaline disruption of the virion. Nicked viral DNA or linear DNA are largely free of protein. Most of the viral protein disruption is in the form of capsomeres, sedimenting principally at 105 and 7S. Despite the relatively constant ratio of 10S to 7S material in many preparations, (1:5.5 to 1:6.0, respectively), the two classes of capsomeres are indistinguishable by electron microscopy and contain only P2, P3, and P4 in molar ratios of approximately 5: 1:1 or 6:1: 1, respectively. Material with sedimentation rates of approximately 1 to 3S is enriched for P1 and contains small amounts of P2, P3, and P4. During the in vitro reassembly of DNA-free, shell-like particles from disrupted virus, proteins P1, P2, P3, P4 , and P7 are reincorporated efficiently, whereas P5 and P6 are not. The presence in empty reassembled particles of histone-like protein, expecially P7, implies that at least this one of the minor protein components of the virion may participate in protein-protein interactions with other components of the capsid.

Characterization of a DNA-protein complex and capsomere subunits derived from polyoma virus by treatment with ethyleneglycol-bis-N,N'-tetraacetic acid and dithiothreitol

“…1, 2, and 8). Both the DNA-protein complex and the capsomeres are substantially different than those previously described using other in vitro dissociation systems (4,9). The experimental evidence presented indicates that the polyoma EGTA-DTT dissociation products are not artifacts of the dissociation procedure.…”

“…Evidence is presented in this report which substantiates the association of specific polyoma virion proteins within the 48S complex. The 48S sedimentation value is significantly larger than that of 21S naked polyoma DNA or the 25 to 30S DNA-protein complex isolated from carbonate-treated virions (9). The 48S complex is not formed by the nonspecific association of capsomere proteins with 21S viral DNA (data not shown).…”

“…Previously, the virion capsomere subunits obtained by alkaline carbonate dissociation of polyoma virions were repored to sediment as 7S and 10S subunits and contain the structural proteins VP1, VP2, and VP3 (9). There was approximately five to six copies of VP1, one copy of VP2, and one copy of VP3 in both species of capsomeres.…”

“…However, at the present time there is a great deal of uncertainty as to how the different polypeptides fit into the virion structure. The histones are closely associated with the internal viral DNA of the particle (9,18), but are also believed to be external on the capsid structure (11,12,16,20). The involvement of proteins VP1, VP2, and VP3 in the capsid structure and their relationship to the hexons and pentons is unknown.…”

“…dissociation procedure is dependent upon the chelation of Ca2" ions that are found associated with the virion and the disruption of disulfide bonds. This dissociation procedure may be carried out under more physiological conditions than could previously described systems (8,9,23) and has proven to be advantageous in dissecting the structure of the virion. The purpose of this paper is to describe the biophysical and biochemical properties of the DNA-protein complex and capsomere subunits which are released by this dissociation technique.…”