MUTATIONAL ANALYSIS OF THE VIRION HOST SHUTOFF GENE (UL41) OF HERPES-SIMPLEX VIRUS (HSV) - CHARACTERIZATION OF HSV TYPE-1 (HSV-1) HSV-2 CHIMERAS/

During lytic herpes simplex virus (HSV) infections, the half-lives of host and viral mRNAs are regulated by the HSV virion host shutoff (Vhs ) protein (UL41). The sequences of the UL41 polypeptides of HSV type 1 (HSV-1) strain KOS and HSV-2 strain 333 are 87% identical. In spite o f this similarity, HSV-2 strains generally shut off the host more rapi dly and completely than HSV-1 strains, To examine type-specific differ ences in Vhs function, we compared the Vhs activities of UL41 alleles from HSV-1(KOS) and HSV-2(333) by assaying the ability of a transfecte d UL41 allele to inhibit expression of a cotransfected reporter gene, Both HSV-1 and HSV-2 alleles inhibited reporter gene expression over a range of vhs DNA concentrations. However, 40-fold less of the HSV-2 a llele was required to yield the same level of inhibition as HSV-1, ind icating that it is significantly more potent. Examination of chimeric UL41 alleles containing various combinations of HSV-1 and HSV-2 sequen ces identified three regions of the 333 polypeptide which increase the activity of KOS when substituted for the corresponding amino acids of the KOS protein, These are separated by two regions which have no eff ect on KOS activity, even though they contain 43 of the 74 amino acid differences between the parental alleles, In addition, alleles encodin g a full-length KOS polypeptide with a 32-amino-acid N-terminal extens ion retain considerable activity. The results begin to identify which amino acid differences are responsible for type-specific differences i n Vhs activity.