The herpes simplex virus (HSV) thymidine kinase (tk) gene provides an excellent model system for studies of eukaryotic gene expression. The long term goal of these studies is to understand mechanisms regulating tk expression during HSV infection. The specific questions we wish to investigate-include: 1) The roles of two GC rich sequences in the tk promoter that bind transcription factors such as Sp1 in the induction of tk transcription; 2) The role of a region that reportedly contains a conserved octanucleotide sequence that functions to increase tk promoter activity in uninfected cells; 3) Whether a mutation that increase tk transcription in frog oocytes can increase tk transcription during HSV infection, and if so, whether it increases tk mRNA levels; 4) The sequence alteration of a likely tk promoter point mutation; 5) The sequences in a transcription signal that is downstream of the mRNA cap site that affects tk transcription; and 6) The effects of tk expression on the expression of neighboring genes that overlap its 5' and 3' ends. The methods we will use will be similar to those we have used previously. We will construct HSV mutants that contain mutations in relevant sequences and analyze them and members of our previous collection of HSV linker scanning mutants for their effects on the expression of tk and neighboring genes. HSV and other herpesviruses cause several diseases for which there are limited treatments, but no cure. Information regarding the properties of the tk gene and the mechanisms of gene expression in HSV infection may lead to better anti-herpesvirus agents.