Chromosome replication origins: Do we really need them?

Abstract

Replication of the main chromosome in the halophilic archaeon Haloferax volcanii was recently reported to continue despite deletion of all active replication origins. Equally surprising, the deletion strain grew faster than the parent strain. It was proposed that origin-less H. volcanii duplicate their chromosomes via recombination-dependent replication. Here, we recall our present knowledge of this mode of chromosome replication in different organisms. We consider the likelihood that it accounts for the viability of H. volcanii deleted for its main specific replication origins, as well as possible alternative interpretations of the results. The selective advantages of having defined chromosome replication origins are discussed from a functional and evolutionary perspective.

Too Much of a Good Thing: How Ectopic DNA Replication Affects Bacterial Replication Dynamics

“…The deletion of single origins resulted in only mild growth rate reductions (Hawkins et al, 2013), as observed in other archaea (Samson et al, 2013;Wu et al, 2014). In contrast, deletion of multiple origins resulted in improved growth rates, and a derivative in which all replication origins were deleted grew faster than wild type cells, an effect that appears to be driven by recombination-dependent replication (Hawkins et al, 2013), replication that initiates at recombination intermediates (Hawkins et al, 2013;Michel and Bernander, 2014).…”

Rolf Bernander (1956–2014): pioneer of the archaeal cell cycle

“…H. volcanii was later found to be in possession of a third origin, and was remarkably also shown be able to replicate with all three origins deleted (Hawkins et al ., ). Rolf discussed the implications of this finding in a posthumously published article (Michel and Bernander, ).…”

DNA Replication Restart in Archaea

“…An alternative explanation for RDR is activation of dormant origins randomly in cells so that no preferential origin emerged at the level of a cell population [29,30]. In this scenario the essentiality of RadA could imply that randomly-initiated replication forks more often collapse and have to be restarted.…”