Isolation and partial characterization of nucleocapsid forms from cells infected with human cytomegalovirus strains AD169 and Towne.

We characterized nucleocapsid (NC) forms generated during infection with human cytomegalovirus (HCMV) strains AD169 and Towne. Two morphological forms of NC were isolated by Renografin-76 banding of the nuclear (N) or cytoplasmic (C) fractions of infected cells. SDS-PAGE analysis of the N- and C-NC forms of AD169 and Towne showed the presence of three polypeptides (150, 33, and 30 KD). The C-NC contained five additional polypeptides (260, 112, 110, 68, and 54 KD) with a counterpart in the mature virion. An additional polypeptide of 37 KD (Towne) or 39 KD (AD169) was only present in the B-NC and not in the A-NC, C-NC, or the mature virion. These polypeptides were basic as determined by two-dimensional PAGE analysis. The 37-KD (Towne) and the 39-KD (AD169) polypeptides were phosphorylated. The NC polypeptides were HCMV specific as shown by immunoprecipitation using a pool of HCMV-positive human antisera. The B-NC DNA was shown to have a restriction pattern identical to that of the infectious viral DNA, but no DNA was detected in the A-NC form. Analysis of NC forms by pulse-chase experiments identified a 'pre-NC' peak which may serve as a precursor to the A- and B-NC forms.