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
DNA replication the levels of protein DnaA. All these control the binding of initiator proteins to the origin sequences. Because "E. coli" methylates GATC DNA sequences, DNA synthesis results in hemimethylated sequences. This hemimethylated DNA is recognized by the protein 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. ATP builds up when the cell is in a rich medium, triggering DNA replication once the cell has reached a specific size. ATP competes