ANALYSIS OF DNA METHYLATION PROCESSES RELATED TO THE INHIBITION OF DNA-SYNTHESIS BY 5-AZACYTIDINE IN STREPTOMYCES-ANTIBIOTICUS ETH-7451

5-Azacytidine inhibits DNA synthesis and to a lesser proportion RNA sy nthesis in S. antibioticus. The biosynthesis of proteins is not affect ed. The main inhibitory effect of 5-azacytidine on DNA and RNA synthes is is probably caused by its incorporation into newly synthesized DNA or RNA and the formation of covalent complexes between cytosine-specif ic methyltransferases and the modified DNA or RNA templates. To analyz e whether such effects could occur at the oriC region of S. antibiotic us we analyzed the methylation status of this region using the bisulph ite assisted genomic sequencing method. One of the cytosine residues f ound to be partially methylated was contained within an unique Nael se quence (GCCGGC) in oriC. Subsequent analysis shows chromosomal DNA fro m S. antibioticus to be resistant to R.Nael restriction indicating tha t this strain contains a Nael-specific cytosine C5-methyltransferase a ctivity. Following 5-azacytidine treatment the Nael site within the or iC region becomes partially demethylated. Our results suggest that som e of the 5-azacytidine effects on DNA and RNA synthesis might indeed b e related to the complex formation and inhibition of a cytosine-specif ic DNA methyltransferase.