THE REGULATION OF SYNTHESIS AND PROPERTIES OF THE PROTEIN PRODUCT OF OPEN READING FRAME-P OF THE HERPES-SIMPLEX VIRUS-1 GENOME

Open reading frame P (ORF P) maps in the inverted repeat sequence ab a nd b'a' banking the long unique (U-L) sequence of the herpes simplex v irus 1 genome, within the sequence reported to be transcribed during l atent infection of sensory neurons. Both the protein and the RNA were previously reported to be expressed only in cells infected with a dele tion mutant or with a mutant carrying a ts lesion in the alpha 4 gene encoding the infected cell protein no. 4 (ICP4), a major regulatory pr otein of the virus. In this report we show that (i) disruption of the ICP4 DNA binding site by replacement mutagenesis resulted in the overe xpression of ORF P protein even at permissive temperatures, leading to productive infection; (ii) the expression of ORF P does not require p rior viral protein Synthesis; (iii) late in infection the ORF protein P is processed into multiple forms characterized by a slower electroph oretic mobility in denaturing gels; (iv) ORF P protein accumulates in nuclei of infected cells; and (v) in some nuclei of infected cells, OR F P protein is organized in the form of rods traversing the nucleus fr om the basolateral to the apical side. We conclude that ORF P has many of the properties predictive of a viral gene group, which we designat e pre-alpha. Specifically, these could be induced by the alpha transin ducing factor (also known as VP16) carried in the virion; they would b e firmly shut off by the onset of expression of alpha genes required f or productive infection; and in the absence of repressive effects of I CP4, their expression could be dependent on the number of viral DNA co pies available for transcription. Finally, the productively infected c ell would evolve a way of disposing excess pre-alpha proteins by postt ranslational processing.