The relationship between sequence-specific termination of DNA replication and transcription

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Replication fork arrest in prokaryotes like Escherichia coli and Bacillus subtilis occurs at specific DNA sequences in the terminus.
• Replication terminator proteins bind to these sites, causing polar arrest of replication forks by inhibiting replicative helicases in a unidirectional manner (polar contrahelicase activity).

Purpose of the Study:

• To investigate a second, previously unreported activity of replication terminator proteins from E. coli and B. subtilis.
• To characterize the ability of these proteins to impede RNA chain elongation by prokaryotic RNA polymerases.

Main Methods:

• Tested the effect of E. coli ter and B. subtilis RTP proteins on RNA chain elongation.
• Utilized T7, SP6, and E. coli RNA polymerases in assays to assess RNA polymerase activity.
• Determined the stoichiometry of protein required for activity (one ter monomer, two RTP dimers).

Main Results:

• Replication terminator proteins ter (E. coli) and RTP (B. subtilis) were found to block RNA chain elongation by multiple prokaryotic RNA polymerases.
• This RNA chain anti-elongation activity, like contrahelicase activity, occurred in a polar fashion.
• Different protein oligomerization states were required: one ter monomer or two interacting RTP dimers were sufficient for blockage.

Conclusions:

• Prokaryotic replication terminator proteins possess a dual function: polar contrahelicase activity and polar RNA chain anti-elongation activity.
• This RNA chain anti-elongation activity is biologically significant, preventing the functional inactivation of replication arrest sites by invading transcription.
• Restricting transcription passage through the terminus-terminator protein complex is essential for maintaining replication termination fidelity.