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The initiator proteins are the proteins that recognize a specific DNA sequence within the origin of replication. The origin of replication is the site where the helicase attaches to the template strand and starts to unwind the DNA into two strands.
The replication initiator protein (Rep) plays a key role in initiation of replication in plasmids. In its monomer form, Rep binds an iteron and promotes replication. The protein itself is known to contain two independent N-terminal and C-terminal globular domains that subsequently bind to two domains of the iteron.
More than five decades ago, Jacob, Brenner, and Cuzin proposed the replicon hypothesis to explain the regulation of chromosomal DNA synthesis in E. coli. [18] The model postulates that a diffusible, trans-acting factor, a so-called initiator, interacts with a cis-acting DNA element, the replicator, to promote replication onset at a nearby origin.
DnaA is a protein that activates initiation of DNA replication in bacteria. [1] Based on the Replicon Model, a positively active initiator molecule contacts with a particular spot on a circular chromosome called the replicator to start DNA replication. [2] It is a replication initiation factor which promotes the unwinding of DNA at oriC. [1]
[11] [10] In E. coli the primary initiator protein is Dna A; in yeast, this is the origin recognition complex. [27] Sequences used by initiator proteins tend to be "AT-rich" (rich in adenine and thymine bases), because A-T base pairs have two hydrogen bonds (rather than the three formed in a C-G pair) and thus are easier to strand-separate. [28]
A licensing factor is a protein or complex of proteins that allows an origin of replication to begin DNA replication at that site. Licensing factors primarily occur in eukaryotic cells, since bacteria use simpler systems to initiate replication. However, many archaea use homologues of eukaryotic licensing factors to initiate replication. [1]
The ORC4 protein is known to bind the AT-rich portion of the origin of replication in S. pombe using AT hook motifs. The mechanism of origin recognition in higher eukaryotes is not well understood but it is thought that the ORC1-6 proteins depend on unusual DNA topology for binding.
When Mcm2-7 is first loaded it completely encircles the DNA and helicase activity is inhibited. 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 ...