Caffeine, at doses which enhance killing by UV light, inhibits the biosynthesis of pyrimidines in Chinese hamster ovary cells (K1) in culture. This inhibition was measured as a decrease in [14C]UTP and [14C]CTP accumulation after a 3-h incubation with [14C]aspartate or [14C]orotate and a similar decrease in Urd-A cells (which lack the first three enzymes of the pathway) using [14C]orotate as su...

The construction of deletion-knockout poxviruses is a useful approach to determining the function of specific virus genes. This protocol is an adaptation of the transient dominant knockout selection protocol published by Falkner and Moss (1990) for use with vaccinia virus. The protocol makes use of the dominant selectable marker Escherichia coli guanine phosphoribosyltransferase (gpt) gene (Mul...

The genotoxicity of benzo(a)pyrene (BP) was investigated in combined cultures of rat hepatocytes and human diploid fibroblasts. Freshly isolated rat hepatocytes were shown to activate BP to a species which bound to and damaged hepatocyte and fibroblast DNA. A significant increase in the hypoxanthine-guanine phosphoribosyltransferase mutation frequency was induced when 10 to 100 microM BP was ad...

It has been demonstrated that restriction fragment length polymorphisms of X-chromosome genes can be used in conjunction with methylation patterns to determine the clonal composition of human tumors. In this report, we show that several X-chromosome probes can be used for such analyses. In particular, probes derived from the hypoxanthine phosphoribosyltransferase gene and the phosphoglycerate k...

The measurement of the activity of the X-linked enzyme HPRT has been widely used as an indicator of X-chromosome activity during preimplantation development in the mouse. More recently, the concomitant measurement of the activity of the autosomally-encoded enzyme APRT has been used in an attempt to decrease the variability inherent in the measurement of enzyme activity from minute samples such ...