User:Bianca Varney/Bacterial Replication Termination
From Proteopedia
Bacterial replication termination is mediated by replication terminator proteins that bind to polar inverted repeats approximately 180 degrees from the origin of replication (OriC).Replication terminator proteins bind bacterial DNA at termination (Ter) sites. When the replication forks meet with terminator proteins bound to Ter sites, replication is arrested, and DNA polymerase falls off the bacterial chromosome. However, protein-Ter interactions are orientation specific, and will only arrest the replication forks traveling in on one direction; either clockwise or anticlockwise. This means that one replication fork will be arrested at a Ter site, while the other fork, traveling in the opposite direction, will pass through the site unimpeded, allowing the entire bacterial chromosome to be copied. The area loaded with Ter sites in the chromosome is called a "replication fork trap".
Mechanism
Bacterial replication termination has been well studied in E. coli and B. subtilis. The proteins involved in this termination process differ structurally in these two bacterium, although each contains similar contrahelicase activity and performs similar functions in arresting replication. The replication termini sequences are located in two clusters approximately 180 degrees from the origin of replication, and are orientated such that each cluster has opposite polarity and are therefore inverted repeats. This means that counterclockwise replication forks can move beyond the first cluster of ter sites, the left terminus, but are arrested at the second cluster, the right terminus, containing correct polarity. Similarly, the clockwise fork will proceed through the left cluster but will be arrested at the right. The bipartite Ter nucleotide sequence is overlapping and each inverted repeat contains a core (IRIB) and an axillary (IRIA) sites. RTP binds to these sequences, resulting in the impediment the replication fork helicase.
