Transcription from Complementary Deoxyribonucleic Acid Strands in Various Sporogenic and Asporogenic Mutants of Bacillus subtilis

The present paper describes an investigation, at the transcription level, in a thermosensitive sporulation mutant of Bacillus subtilis (ts‐4) grown at the permissive (30 °C) or restrictive (42 °C) temperature where sporulation capacity is respectively expressed or arrested. These studies were carried out by analysing the ribonucleic acid from vegetative and stationary phase cells (t 3 cells) grown under both conditions, by hybridization‐competition experiments. It was found that about 32 % of t3 RNA species synthesized on the heavy (H) strand and about 19% of those synthesized on the light (L) strand have distinct sequences, depending on the growth conditions of the ts‐4 cells: permissive or restrictive conditions. No such difference was observed in a normal zero‐stage asporogenic mutant grown under the same conditions. These results suggest, therefore, that at the restrictive temperature the block in sporulation capacity of this mutant might, at least partially, reside in a deficiency at the transcription level. The significance of transcription from the L strand of B. subtilis DNA reported by others was also investigated. Based on our hybridization‐competition studies on different sporogenic and asporogenic mutants it was suggested that the expression of some vegetative genes on the L strand during sporulation might have a regulatory function in the ‘switch‐on’ of spore genes on the H stand.