Localization of (dA-dT)-rich sequences in the membrane-bound DNA and their possible role in sporulation of Bacillus polymyxa

Abstract

The appearance of poly(A)RNA species at the onset of sporulation has been demonstrated in B. polymyxa. These RNA species, characterized by short oligo(A) stretches, are synthesized at the end of exponential growth (t0) and their level reaches a maximum two hours later (t2 of sporulation). This new feature of sporulation appears relevant to this process as indicated by the lack of formation of poly(A)RNA in mutants blocked at the early stages of sporulation. In addition, the antibiotic netropsin, which is known to inhibit sporulation without affecting the vegetative growth of B. subtilis, also inhibits poly(A) RNA synthesis and sporulation in B. polymyxa. The selective inhibitory effect of netropsin on the poly(A)RNA formation, as reflected in the reduced incorporation of [3H]-adenosine into RNA by sporulating cells, is traced to the inhibition of sporulation-specific RNA polymerase under in vitro conditions. The inhibition of transcription concerns mainly the DNA regions that are firmly associated with membranes. Moreover, [32P]-labeled poly(A)RNA isolated from sporulating cells at t2 hybridizes preferentially with membrane bound DNA (mDNA). Further evidence that the mDNA is enriched in d(AT) sequences was obtained by demonstration of the resistance of the mDNA-netropsin complex to DNase action. Based on the property of netropsin to bind to AT sequences in DNA, it is proposed that early spore genes might be enriched in d(AT) sequences and are localized in mDNA.