Analysis in Bacillus subtilis phage 2C DNA of the abnormal base hydroxymethyluracil, and its replacement by thymine in thermosensitive mutants

2C is a lytic phage of Bacillus subtilis, having hydroxymethyluracil (hmUra) replacing thymine (T) in its genome. Little is known of the metabolic advantages of this substitution, in particular for the cascade of regulatory factors ensuring efficient transcription of early, middle and late promoters. Here we report on the isolation of thermosensitive 2C mutants, which could be subdivided in three classes: (1) mutants having 75% replacement of hmUra by thymine in the restrictive conditions; (2) mutants unable to inhibit B. subtilis DNA synthesis in the course of infection, (3) mutants with reduced viral DNA biosynthesis. Different techniques led to these conclusions: differential binding of chromofluorophores with hmUra- and T-containing DNA, quantification of viral DNA by hybridization and buoyant density analysis of labeled DNA in CsCl gradients. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.