Mechanism of dnaB protein action. IV. General priming of DNA replication by dnaB protein and primase compared with RNA polymerase.

The general priming system of dnaB protein and primase (Arai, K., and Kornberg, A. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 4308-4312) when compared with priming by RNA polymerase shows a number of striking differences. The general priming system is initiated primarily at single-stranded region(S), being active only on single-stranded DNAs (phages and homopolymers) and inhibited by single-stranded DNA binding protein (SSB). Transcripts are only 10 to 60 residues long. By contrast, RNA priming by RNA polymerase is initiated at base-paired regions that are not destabilized by SSB (Geider, K., Beck, E., and Schaller, H. (1978) Proc. Natl. Acad. Sci. U. S. A. 76, 645-649) and transcripts on DNA not coated with SSB are generally longer. In general priming, ATP (or GTP) has three functions: (i) an allosteric effect on dnaB protein in which the nonhydrolyzed analogs adenosine-5'-O-(3'-thiotriphosphate) (or guanosine-5'-O-(3'-thiotriphosphate) can substitute, (ii) initiation of primer synthesis which can incorporate deoxy-, as well as ribonucleotides, and (iii) elongation of the primer, in which the beta, gamma-imido analog can replace ATP (or GTP). An allosteric effect of ATP on RNA polymerase has not been demonstrated, nor has the facile synthesis of hybrid transcripts of ribo- and deoxyribonucleotides.