Extrachromosomal DNA membrane bound nucleus like the eukaryotes, they do contain a nucleoid region in which the main chromosome is found. Extrachromosomal DNA exists in prokaryotes outside the nucleoid region as circular or linear plasmids. Bacterial plasmids are typically short sequences, consisting of 1 kilobase (kb) to a few hundred kb segments, and contain an origin of replication which allows the plasmid to replicate independently of the bacterial chromosome. The total number of a particular plasmid within a cell is referred to as the copy number and can range from as few as two copies per cell to as many as several
Eukaryotic DNA replication formation of single-stranded DNA occurs frequently, more often during replication stress. ATR-ATRIP is able to arrest the cell cycle to preserve genome integrity. ATR is found on chromatin during S phase, similar to RPA and claspin. The generation of single-stranded DNA tracts is important in initiating the checkpoint pathways downstream of replication damage. Once single-stranded DNA becomes sufficiently long, single-stranded DNA coated with RPA are able to recruit ATR-ATRIP. In order to become fully active, the ATR kinase rely on sensor proteins that sense whether the checkpoint proteins are localized to a valid site of DNA replication stress. The RAD9-HUS1-Rad1