Interaction between the antibiotic tyrocidine and DNA in vitro

Abstract

VERY little is known about the natural function of the peptide antibiotics. The production of antibiotics may be related to sporulation as only sporulating microorganisms produce antibiotics¹. In general, the synthesis of antibiotics occurs within a limited time at the end of the logarithmic growth of cell cultures², concurrent with a change in the specificity of transcription³. Loss, through mutation, of the ability to synthesise the antibiotic leads to asporogeny, in some cases¹. Specific inhibitors and changes in culture conditions affect both the synthesis of antibiotic and sporulation⁴. Sarkar and Paulus⁵ demonstrated that the cyclic peptide antibiotic, tyrocidine, produced by Bacillus brevis (ATCC 8185) effects RNA synthesis in vivo, whereas DNA synthesis continues. Moreover, these authors give evidence that tyrocidine inhibited an in vitro RNA transcriptional system using B. brevis DNA and B. brevis DNA-dependent RNA polymerase. Complete inhibition of RNA synthesis with a tyrocidine concentration comparable to that in a B. brevis cell at the end of the vegetative growing phase was observed. A strong binding of the oligopeptide antibiotics, neotropsin and distamycin A, to double-stranded DNA, resulting in a pronounced heat stabilisation of the double-strands, has been reported⁶. Compared with pure DNA, these peptide-DNA complexes exhibit a low template activity⁷.