Sequences that are involved with termination are called ter sites. A ter site contains a short, -23-bp sequence.

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#Unit 3. Fundamental Processes

The ter site is recognized by a unidirectional contrahelicase (called Tus in E. coli and RTP in B. subtilis) that recognizes the consensus sequence and prevents the replication fork from proceeding.

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#Unit 3. Fundamental Processes

The E. coli enzyme acts by antagonizing the replication helicase in a direction a) manner by direct contact between the DnaB helicase and Tus.

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#Unit 3. Fundamental Processes

Deletion of the ter sites does not, however, prevent normal replication cycles from occurring, although it does affect segregation of the daughter chromosomes.

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#Unit 3. Fundamental Processes

The two replication forks meet and halt in a region approximately halfway around the chromosome from the origin.

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#Unit 3. Fundamental Processes

 In E. coli, two clusters of five ter sites each, including terk, -I, -E, -D, and -A on one side and terC, -B, -F, -G, and -H on the other, are located -100 kb on either side of this termination region.