Abstract
The alteration in the DNA sequence responsible for the mutant phenotype of the herpes simplex virus type 1 temperature-sensitive mutant ts K has been determined. A single C:G base pair present in the wild-type Vmw 175 immediate-early polypeptide-coding sequence has been replaced by T:A in the mutant gene. This results in the substitution of an alanine by a valine codon. In two revertants the mutant T:A base pair has been resubstituted by C:G.