“…It has been reported that rif'ampin, an inhibitor of ribonucleic acid (RNA) polymerase, blocks the conversion of M13 single-strand DNA to the replicative form (2,35,38,39), but fails to block the synthesis of' X174 replicative form (38). It has been f'urther reported that a transcriptional step is directly involved in DNA replication of' various replicons: phage X (7,15,32), T7 (10), colEl (3,4,30,31), F (17,18), R64-11 (8), plasmid of E. coli 15 (22), plasmid of' Salmonella pullorum ( 16), E. coli (12, 13, 19, 21; T. Saitoh and S. Hiraga, accepted for publication), and Bacillus subtilis (20,23).…”