Labeling the deoxyribonucleic acid of Anacystis nidulans

Analysis of cell-free extracts of Anacystis nidulans disclosed the absence of both thymidine phosphorylase (EC 2.4.2.4) and thymidine kinase (EC 2.7.1.21) activities. Thymine and thymidine were incorporated inefficiently by intact cells of A. nidulans either in the presence or absence of deoxyguanosine (250 mug/ml). Deoxythymidine monophosphate incorporation was also inefficient. Radioactive deoxyadenosine, at a minimally toxic level (3 mug/ml), was incorporated effectively into the deoxyribonucleic acid (DNA). A cesium chloride-ethidium bromide gradient analysis of the DNA revealed that both the plasmid DNA and the principal DNA of the A. nidulans genome were labeled effectively in cells exposed to [8-14C]deoxyadenosine.