An 85-kilodalton herpes simplex virus type 1 alpha trans-induction factor (VP16)-VP13/14 fusion protein retains the transactivation and structural properties of the wild-type molecule during virus infection

Abstract

The 65-kDa herpes simplex virus type 1 encoded a trans-induction factor (aTIF or VP16) has two important functions: it is required for the efficient transcriptional induction of the a or immediate-early genes, and it acts as an essential structural component of the virion. The transcription properties of oiTIF have been well studied in vitro. The protein is a powerful inducer of RNA polymerase 1I-directed transcription and, similar to the cellular transcriptional transactivators GAL4 and CGN4, contains separable DNA binding and transactivation domains. In contrast, little is known about the structural function of oTIF because this function can be studied only during virus replication and structural mutants are lethal. The in vivo analysis of oxTIF is further complicated by the likelihood that the transcription and structural functions are not entirely separable. In this study, we take an alternate approach toward the development of oTIF mutants and their subsequent characterization. Rather than analyzing the effects of intragenic mutations, we have examined the properties of a mutant virus which expresses an oTIF fusion protein containing 61 amino acids of another herpes simplex virus type 1 virion protein, VP13/14, fused to its C terminus. This is the first report which demonstrates that the C-terminus of oTIF can tolerate the addition of an adjacent protein domain without compromising its transactivation function in vivo. Moreover, the VP13/14 sequences do not interfere with the protein-protein interactions required for virion targeting and assembly.

Expression and function of the equine herpesvirus 1 virion-associated host shutoff homolog

“…While it is possible that the lack of vhs activity during EHV-1 infection is due to a reduced concentration of the ORF19 protein per viral particle compared with that of HSV-1 vhs, no direct conclusions can be drawn from the present study concerning the relative concentration of the virion-associated ORF19 protein compared with that of HSV-1 vhs. However, in this regard, it should be noted that wild-type HSV-1 vhs also is a relatively minor viral component; it has been estimated that there are approximately 200 vhs molecules per viral particle (46,47), compared with 1,000 to 2,000 copies of the abundant tegument protein, VP16, the ␣ gene transinducing factor (␣TIF [23]). Further studies to compare the relative amounts of these proteins as well as the transcriptional efficiencies of UL41 and ORF19 are underway.…”