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J. Virol., Feb 1997, 1281-1291, Vol 71, No. 2
NL Oien, DR Thomsen, MW Wathen, WW Newcomb, JC Brown and FL Homa
An essential step in assembly of herpes simplex virus (HSV) type 1 capsids
involves interaction of the major capsid protein (VP5) with the C terminus
of the scaffolding protein (encoded by the UL26.5 gene). The final 12
residues of the HSV scaffolding protein contains an A-X-X-F-
V/A-X-Q-M-M-X-X-R motif which is conserved between scaffolding proteins
found in other alphaherpesviruses but not in members of the beta- or
gamma-herpesviruses. Previous studies have shown that the bovine
herpesvirus 1 (alphaherpesvirus) UL26.5 homolog will functionally
substitute for the HSV UL26.5 gene (E. J. Haanes et al., J. Virol.
69:7375-7379, 1995). The homolog of the UL26.5 gene in the human
cytomegalovirus (HCMV) genome is the UL80.5 gene. In these studies, we
tested whether the HCMV UL80.5 gene would substitute for the HSV UL26.5
gene in a baculovirus capsid assembly system that we have previously
described (D. R. Thomsen et al., J. Virol. 68:2442-2457, 1994). The results
demonstrate that (i) no intact capsids were assembled when the full-length
or a truncated (missing the C-terminal 65 amino acids) UL80.5 protein was
tested; (ii) when the C-terminal 65 amino acids of the UL80.5 protein were
replaced with the C-terminal 25 amino acids of the UL26.5 protein, intact
capsids were made and direct interaction of the UL80.5 protein with VP5 was
detected; (iii) assembly of intact capsids was demonstrated when the
sequence of the last 12 amino acids of the UL80.5 protein was changed from
RRIFVA ALNKLE to RRIFVAAMMKLE; (iv) self-interaction of the scaffold
proteins is mediated by sequences N terminal to the maturation cleavage
site; and (v) the UL26.5 and UL80.5 proteins will not coassemble into
scaffold structures. The results suggest that the UL26.5 and UL80.5
proteins form a scaffold by self-interaction via sequences in the N termini
of the proteins and emphasize the importance of the C terminus for
interaction of scaffold with the proteins that form the capsid shell.
Copyright © 1997, American Society for Microbiology
Assembly of herpes simplex virus capsids using the human cytomegalovirus scaffold protein: critical role of the C terminus
Pharmacia & Upjohn, Inc., Kalamazoo, Michigan 49007, USA.
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