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

Herpes simplex virus type 1 (KOS)Delta gK is a mutant virus which lacks glycoprotein K (gK) and exhibits defects in virion egress (S. Jayachandra, A. Baghian, and K. G. Rousoulas, J. Virol. 69:5401-5413, 1997). To further understand the role of gK in virus egress, we constructed recombinant viruses, Delta gKhpd-1, -2, -3, and -4, that specified gK amino-terminal portions of 139, 239, 268, and 326 amino acids, respectively, corresponding to truncations immediately after each of the four putative membrane-spanning domains of gK. Delta gKhpd-1 and Delta gKhpd-2 viruses produced lower yields and smaller plaques than Delta gK. Numerous Delta gKhpd-1 capsids accumulated predominately within large double-membrane vesicles of which the inner membrane appeared to be derived from viral envelopes while the outer membrane appeared 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 carboxy-terminal 12 amino acids did not adversely affect virus replication and egress. Comparisons of the gK primary sequences specified by alphaherpesviruses revealed the presence of a cysteine-rich motif (CXXCC), located within domain III in the lumen side of gK, and a tyrosine-based motif, YTK Phi (where Phi,is any bulky hydrophobic amino acid), located between the second and third hydrophobic domains (domain II) in the cytoplasmic side of gK. The mutant virus gK/Y183S, which was constructed to specify gK with a single-amino-acid change (Y to S) within the YTK Phi, motif, replicated less efficiently than the Delta gK virus. The mutant virus gK/C304S-C307S, which was constructed to specify two serine instead of cysteine residues within the cysteine-rich motif (CXXCC changed to SXXSC) of gK domain III, replicated more efficiently than the Delta gK virus. Our data suggests that gK contains domains in its amino-terminal portion that promote aberrant nucleocapsid envelopment and/or membrane fusion between different virion envelopes and contains domains within its domains II and In. that function in virus replication and egress.