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A gene cluster is a group of two or more genes found within an organism's DNA that encode similar polypeptides or proteins which collectively share a generalized function and are often located within a few thousand base pairs of each other. The size of gene clusters can vary significantly, from a few genes to several hundred genes. [1]
One bacterial plasmid used in genetic engineering as a plasmid cloning vector is pUC18. Its polylinker region is composed of several restriction enzyme recognition sites, that have been engineered into a single cluster (the polylinker). It has restriction sites for various restriction enzymes, including EcoRI, BamHI, and PstI.
A typical operon. In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. [1] The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splicing to create monocistronic mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product.
Here, replication origins gather into bundles called replicon clusters. Each cluster's replicons are similar in length, but individual clusters have replicons of varying length. These replicons all have similar basic residues to which the ORC binds, which in many ways mimic the conserved 11bp A element.
A bacterial chromosome contains a single origin, and therefore the whole bacterial chromosome is a replicon. The chromosomes of archaea and eukaryotes can have multiple origins of replication, and so their chromosomes may consist of several replicons [citation needed].
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.
However this is ruled out because GTA particles are typically too small to contain the genes that encode them. For example, the main RcGTA cluster (see below) is 14 kb long, but RcGTA particles can contain only 4–5 kb of DNA. Most bacteria have not been screened for the presence of GTAs, and many more GTA systems may await discovery.
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]