Characterization of a multienzyme complex derived from a Bacillus subtilis DNA-membrane extract that synthesizes RNA and DNA precursors.

The activity of a variety of enzymes involved in the synthesis of RNA and DNA precursors was found to copurify with initiation of DNA replication activity. These enzymes included ribo- and deoxyribonucleoside kinases, kinases for their phosphorylated intermediates, and ribonucleoside diphosphate reductase. This precursor-synthesizing complex is part of a Bacillus subtilis DNA-membrane extract originally shown to contain all of the enzymes and template necessary for initiation of DNA replication (J. Laffan and W. Firshein, J. Bacteriol. 169:2819-2827, 1987). Although the complex incorporated deoxyribonucleoside triphosphates into DNA, deoxyribonucleosides were incorporated even faster, suggesting catalytic facilitation. Both ribonucleosides and deoxyribonucleosides were found by thin-layer chromatography separation to be converted by the complex into their mono-, di-, and triphosphate derivatives. Ribonucleotides were incorporated into DNA via the action of ribonucleoside diphosphate reductase. Some regulatory mechanisms of the kinase system may also be retained by the complex. Electron microscope studies revealed that the precursor-synthesizing-initiation subcomplex is contained within a particulate fraction consisting of different-size vesicles resembling liposomes and that these particles may be structurally important in maintaining the synthetic activity of the subcomplex.