Incorporation of thymine, thymidine, adenine and uracil into nucleic acids of Mycobacterium phlei and its phage.

Like other prototroph bacteria, Mycobacterium phlei was found to incorporate thymine into its DNA very poorly. As a result of a rapid thymidine-to-thymine conversion, thymidine incorporation also proved to be inefficient. Thymidine incorporation could be somewhat enhanced by pretreatment of the cells with uridine. When radioactive adenine, and particularly uracil, were used as precursors, highly labelled DNA could be obtained from the cells, although the majority of radioactivity was found in the RNA. Uracil was thus found to be the most suitable precursor for labelling phage DNA. On the basis of these findings, uracil is recommended for in vivo labelling of Mycobacterium and mycobacteriophage DNA.