Figure 7.

A model for bidirectional replication of oriλ DNA. Following O-some formation, the simultaneous presence of transcribing RNA polymerase and ClpP/ClpX protease leads to the hydrolysis of λ O protein. In contrast, when the preprimosome complex (oriλ:O⋅P⋅DnaB) has been assembled, transcription by RNA polymerase does not result in λ O hydrolysis by the ClpP/ClpX protease. Apparently, transcription stops at the assembled preprimosome complex. Following DnaK/DnaJ/GrpE molecular chaperone machine action, the λ P protein dissociates from the preprimosome complex, thus allowing DnaB helicase to unwind DNA in the left-to-right direction only. We suggest that the additional presence of the ClpP/ClpX protease and transcription at this stage results in efficient hydrolysis of λ O, thus allowing the DnaB helicase to unwind DNA in the right-to-left direction as well, thus resulting in bidirectional λ DNA replication.