Composition and mass of the bacteriophage phi 29 prohead and virion

The protein composition of the Bacillus subtilis bacteriophage phi 29 prohe ad and virion was determined by combustion of gel bands of H-3-labeled prot eins. Copy numbers of individual proteins were calculated relative to the 1 2 copies of the head-tail connector protein. The mean numbers of copies of the major capsid protein in the prohead and virion were 241 and 218, respec tively, approaching the 235 copies determined previously by cryoelectron. m icroscopy. The mean numbers of copies of the dimeric head fiber on the proh ead and virion were 24 and 31, respectively, demonstrating partial occupanc y of the 55 fiber binding sites. Measured copies of neck and tail proteins in the virion included I I of the lower collar, 58 of the appendage, and 9 of the tail; if the true copies of these proteins are 12, 60, and 9, respec tively, the entire neck and tail of phi 29 has quasi-sixfold symmetry. The mass of the fiberless prohead with pRNA was about 14.2 MDa, and the mass of the prohead determined by scanning transmission electron microscopy was co nsistent with the biochemical data. The mass of the fiberless virion contai ning the 12.8-MDa DNA genome was about 30.4 MDa. A full complement of dimer ic fibers on the prohead or virion would increase the mass of the particle by about 3.2 MDa. The data complement studies relating the structure of phi 29 components to dynamic functions in morphogenesis and infection. (C) 200 1 Academic Press.