Synthesis of ribosomal RNA during speculation in Bacillus subtilis

Abstract

SPORULATION in Bacillus subtilis is associated with specific changes in RNA metabolism required for the expression of sporulation genes. Although net RNA synthesis stops abruptly at the end of logarithmic growth (T₀), active turnover and differential transcription of the genome have been demonstrated^1–3. Losick and Sonnenshein⁴ suggested that modifications of RNA polymerase may play a primary role in the regulation of gene expression during the sporulation process. The expression of ribosomal RNA genes during this period has been subject to conflicting reports^1,5–7. The reported turn-off of these genes at the onset of sporulation^5,6 has not been observed in similar experiments⁷. The latter, and the reported changes in template specificity of RNA polymerase^4,8 were shown to be strongly dependent on the nature of the sporulation medium and to a lesser extent on the phenotype (sp⁺ or sp⁻) of the strain^7,8. We have analysed the pattern of synthesis and turnover of stable RNA components in B. subtilis induced to sporulate in the highly defined resuspension medium, SM (ref. 9). We report that rRNA synthesis does continue during sporulation, although at a reduced rate, resulting in the gradual replacement of vegetative rRNA components by similar newly synthesised sporulation species.