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Two replication forks can proceed independently around the DNA ring and when viewed from above the structure resembles the Greek letter "theta" (θ). [ 1 ] [ 2 ] Originally discovered by John Cairns , it led to the understanding that (in this case) bidirectional DNA replication could take place.
Replication is bi-directional and originates at a single origin of replication (OriC). [3] It consists of three steps: Initiation, elongation, and termination. [4] Bidirectional Theta type replication. Most circular bacterial chromosomes are replicated bidirectionally, starting at one point of origin and replicating in two directions away from ...
During the elongation phase of replication, the enzymes that were assembled at oriC during initiation proceed along each arm of the chromosome, in opposite directions away from the oriC, replicating the DNA to create two identical copies. This process is known as bidirectional replication.
Progress of replication forks is inhibited by many factors; collision with proteins or with complexes binding strongly on DNA, deficiency of dNTPs, nicks on template DNAs and so on. If replication forks get stuck and the rest of the sequences from the stuck forks are not copied, then the daughter strands get nick nick unreplicated sites.
Replication begins by a regular bidirectional theta replication at oriL but later in the lytic phase, it switches to a rolling circle method of replication using the host recombination machinery. [ 1 ] [ 11 ] [ 12 ] This results in numerous copies of the genome being present on a single linear DNA molecule called a concatemer.
The origin of replication (also called the replication origin) is a particular sequence in a genome at which replication is initiated. [1] Propagation of the genetic material between generations requires timely and accurate duplication of DNA by semiconservative replication prior to cell division to ensure each daughter cell receives the full ...
In S phase, the Mcm2-7 complex interacts with helicase cofactors Cdc45 and GINS to isolate a single DNA strand, unwind the origin, and begin replication down the chromosome. In order to have bidirectional replication, this process happens twice at an origin. Both loading events are mediated by one ORC via an identical process as the first. [34]
MCM2-7 is required for both DNA replication initiation and elongation; its regulation at each stage is a central feature of eukaryotic DNA replication. [3] During G1 phase, the two head-to-head Mcm2-7 rings serve as the scaffold for the assembly of the bidirectional replication initiation complexes at the replication origin.