A model for initiation at origins of DNA replication.

Many prokaryotic origins resemble E. coli oriC in possessing essential AT-rich sequences, tandemly repeated. The role of these repeats may be in the initial opening of the duplex by the initiator protein, as has been found for the 13-mers in oriC and is implied for the 11-mers of the lambda origin. Regulatory influences on the effective action of the initiator protein of E. coli (dnaA protein) include transcriptional activation of the origin, nucleotide binding and membrane attachment of the protein, and interactions leading to the introduction of helicases to start replication forks.