Genetic analysis of the role of herpes simplex virus type 1 glycoprotein Kin infectious virus production and egress

Herpes simplex virus type 1 (KOS)Delta gK is a mutant virus which lacks gly coprotein K (gK) and exhibits defects in virion egress (S. Jayachandra, A. Baghian, and K. G. Rousoulas, J. Virol. 69:5401-5413, 1997). To further und erstand the role of gK in virus egress, we constructed recombinant viruses, Delta gKhpd-1, -2, -3, and -4, that specified gK amino-terminal portions o f 139, 239, 268, and 326 amino acids, respectively, corresponding to trunca tions immediately after each of the four putative membrane-spanning domains of gK. Delta gKhpd-1 and Delta gKhpd-2 viruses produced lower yields and s maller plaques than Delta gK. Numerous Delta gKhpd-1 capsids accumulated pr edominately within large double-membrane vesicles of which the inner membra ne appeared to be derived from viral envelopes while the outer membrane app eared to originate from the outer nuclear membrane. The mutant virus Delta gKhpd-3 produced higher yields and larger plaques than the Delta gK virus. The mutant virus Delta gKhpd-4 produced yields and plaques similar to those of time wild-type virus strain KOS, indicating that deletion of the carbox y-terminal 12 amino acids did not adversely affect virus replication and eg ress. Comparisons of the gK primary sequences specified by alphaherpesvirus es revealed the presence of a cysteine-rich motif (CXXCC), located within d omain III in the lumen side of gK, and a tyrosine-based motif, YTK Phi (whe re Phi,is any bulky hydrophobic amino acid), located between the second and third hydrophobic domains (domain II) in the cytoplasmic side of gK. The m utant virus gK/Y183S, which was constructed to specify gK with a single-ami no-acid change (Y to S) within the YTK Phi, motif, replicated less efficien tly than the Delta gK virus. The mutant virus gK/C304S-C307S, which was con structed to specify two serine instead of cysteine residues within the cyst eine-rich motif (CXXCC changed to SXXSC) of gK domain III, replicated more efficiently than the Delta gK virus. Our data suggests that gK contains dom ains in its amino-terminal portion that promote aberrant nucleocapsid envel opment and/or membrane fusion between different virion envelopes and contai ns domains within its domains II and In. that function in virus replication and egress.