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Biochim Biophys Acta. 1975 Nov 18;414(1):1-8.

Some characteristics of the DNA-tyrocidine complex and a possible mechanism of the gramicidin action.


1. The cyclic peptide antibiotic tyrocidine which inhibits RNA synthesis in vitro by forming a complex with the DNA (Schazschneider, B., Ristow, H. and Kleinkauf, H. (1974) Nature 249, 757-759) induces hypochromicity of the DNA. The complex dissociates at elevated temperatures but which are below the melting temperature of the DNA. 2. The linear peptide antibiotic gramicidin which reverses the inhibitory effect of tyrocidine (Ristow, H., Schazschneider, B., Bauer, K. and Kleinkauf, H. (1975) Biochim. Biophys. Acta 390, 246-252) does not bind to DNA and does not induce hypochromicity of the DNA. However, the DNA-tyrocidine complex dissociates at lower temperatures when gramicidin is present. Thus gramicidin weakens the binding of tyrocidine to DNA. 3. The presence of DNA quenches the fluorescence of tyrocidine but not that of gramicidin. This quenching of tyrocidine fluorescence is reduced in the presence of gramicidin. 4. Tyrocidine inhibits transcription of single-stranded DNA as well. This inhibition too can be reversed by gramicidin. Thus the action of the peptides is not dependent on a double-stranded DNA conformation.

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