Herpes simplex virus type 1 strain KOS carries a defective US9 and a mutated US8A gene.

The membrane protein encoded by the US9 gene of alphaherpesviruses plays an important role during virion assembly and transport in neurons. Here, we demonstrate that in herpes simplex virus type 1 (HSV-1) strain KOS, due to base substitutions, the predicted TATA-box of US9 is mutated, and a premature stop is present at codon 58 of US9, which contains 91 codons in other HSV-1 strains. The TATA-box mutation also removes the native stop codon of the adjacent US8A gene, leading to extension of the coding region from 160 to 191 codons. Northern blot analyses revealed reduced transcription of US9 in cells infected with HSV-1 KOS. Moreover, a US9-specific antiserum did not detect any gene products in Western blot and immunofluorescence analyses of KOS-infected cells, indicating that the truncated protein is not stable. In contrast, Western blot reactions of a pUS8A-specific antiserum confirmed enlargement of this protein in HSV-1 KOS.