DNA replication in bacteria.

Abstract

Experiments by Cairns (1963), Meselson and Stahl (1958) and others (see review by Bonhoeffer and Messer, 1969) have shown that replication of DNA proceeds sequentially, daughter strands of opposite polarity being synthesised concurrently as a replication fork advances along a replicating DNA molecule. On the other hand the bacterial DNA polymerase characterised by Kornberg and his collaborators (Kornberg, 1969) as well as those found in phage-infected cells and in the tissues of higher organisms, all appear to utilise 5′ deoxynucleoside triphosphates as precursors and to proceed by chain elongation in the 5′-to-3′ direction only (Richardson, 1969). What then is the mechanism by which the daughter strand that runs 3′-to-5′ with respect to the overall direction of replication is synthesised ? One possibility is that its synthesis involves reaction of the 3-OH of deoxynucleoside 5′ triphosphate precursors with a 5′-triphosphate group terminating the growing chain, or reaction of deoxynucleoside 3′-triphosphates with the 5-OH terminus of the growing chain (Mitra and Kornberg, 1966) (Fig. 1 A). However there is no evidence that either type of synthesis can be catalysed by any of the known enzymes, including the recently discovered bacterial DNA polymerase II (see section III), (Richardson, 1969).