Editing DNA replication (section)

=== Bacteria ===
[[File:Hemimethylation.svg|thumb|200px|Dam methylates adenine of GATC sites after replication]]
Most bacteria do not go through a well-defined cell cycle but instead continuously copy their DNA; during rapid growth, this can result in the concurrent occurrence of multiple rounds of replication.<ref>{{Cite journal |vauthors=Tobiason DM, Seifert HS |date=June 2006 |title=The obligate human pathogen, Neisseria gonorrhoeae, is polyploid |journal=PLOS Biology |volume=4 |issue=6 |pages=e185 |doi=10.1371/journal.pbio.0040185 |pmc=1470461 |pmid=16719561 |doi-access=free}}</ref>  In ''E. coli'', the best-characterized bacteria, DNA replication is regulated through several mechanisms, including: the hemimethylation and sequestering of the origin sequence, the ratio of [[Adenosine triphosphate|adenosine triphosphate (ATP)]] to [[Adenosine diphosphate|adenosine diphosphate (ADP)]], and the levels of protein DnaA. All these control the binding of initiator proteins to the origin sequences.<ref>{{Cite journal |last1=O'Donnell |first1=Michael |last2=Langston |first2=Lance |last3=Stillman |first3=Bruce |date=2013-07-01 |title=Principles and concepts of DNA replication in bacteria, archaea, and eukarya |journal=Cold Spring Harbor Perspectives in Biology |volume=5 |issue=7 |pages=a010108 |doi=10.1101/cshperspect.a010108 |issn=1943-0264 |pmc=3685895 |pmid=23818497}}</ref>

Because ''E. coli'' [[DNA methylation|methylates]] GATC DNA sequences, DNA synthesis results in hemimethylated sequences. This hemimethylated DNA is recognized by the protein [[SeqA protein domain|SeqA]], which binds and sequesters the origin sequence; in addition, DnaA (required for initiation of replication) binds less well to hemimethylated DNA. As a result, newly replicated origins are prevented from immediately initiating another round of DNA replication.<ref>{{Cite journal |vauthors=Slater S, Wold S, Lu M, Boye E, Skarstad K, Kleckner N |date=September 1995 |title=E. coli SeqA protein binds oriC in two different methyl-modulated reactions appropriate to its roles in DNA replication initiation and origin sequestration |journal=Cell |volume=82 |issue=6 |pages=927–936 |doi=10.1016/0092-8674(95)90272-4 |pmid=7553853 |s2cid=14652024 |doi-access=free}}<!--|access-date=7 April 2016--></ref>

ATP builds up when the cell is in a rich medium, triggering DNA replication once the cell has reached a specific size. ATP competes with ADP to bind to DnaA, and the DnaA-ATP complex is able to initiate replication. A certain number of DnaA proteins are also required for DNA replication — each time the origin is copied, the number of binding sites for DnaA doubles, requiring the synthesis of more DnaA to enable another initiation of replication.{{cn|date=November 2024}}

In fast-growing bacteria, such as ''E. coli'', chromosome replication takes more time than dividing the cell. The bacteria solve this by initiating a new round of replication before the previous one has been terminated.<ref>{{Cite journal |vauthors=Cooper S, Helmstetter CE |date=February 1968 |title=Chromosome replication and the division cycle of Escherichia coli B/r |journal=Journal of Molecular Biology |volume=31 |issue=3 |pages=519–540 |doi=10.1016/0022-2836(68)90425-7 |pmid=4866337}}</ref> The new round of replication will form the chromosome of the cell that is born two generations after the dividing cell. This mechanism creates overlapping replication cycles.

{{See also|FtsZ|Min System|Plasmid|Plasmid copy number|Plasmid partition system}}