CAPSIDS ARE FORMED IN A MUTANT VIRUS BLOCKED AT THE MATURATION SITE OF THE UL26 AND UL26.5 OPEN READING FRAMES OF HERPES-SIMPLEX VIRUS TYPE-1 BUT ARE NOT FORMED IN A NULL MUTANT OF UL38 (VP19C)

Previously we reported that null mutant viruses of UL19 (VP5) or of UL 18 (VP23), essential components of herpes simplex virus type 1 (HSV-1) capsid shells, do not form precursor capsid structures as judged by s edimentation and electron microscope analysis. A goal of the present e xperiments was to isolate a null mutant virus for the remaining essent ial component of capsid shells, VP19C, encoded by the UL38 open readin g frame (ORF). Furthermore, we wished to determine if a virus altered in the UL26 maturation cleavage site at residues 610 and 611 produced a lethal phenotype. Therefore, we decided to isolate cell lines that e ncode and express multiple capsid genes. Several cell lines were isola ted by transformation of Vero cells and one designated C32 expressed a ll of the essential capsid proteins. Using this cell line we isolated a null mutant virus in the UL38 ORF and a mutant virus that was altere d at residues 610 and 611 of the UL26 and UL26.5 gene products, We fou nd that the null mutant in VP19C did not form a detectable product as judged by sedimentation and electron microscope analyses following inf ection of nonpermissive cells. The mutant virus altered at the UL26 ma turation site resulted in the accumulation of B capsids. Therefore, cl eavage at this site was essential for the maturation of a capsids into C capsids. Interestingly, the absence of cleavage at the maturation s ite was required for the retention of VP24 in the capsid. (C) 1998 Aca demic Press.