ColE1 RNA I is a regulatory RNA that inhibits initiation of DNA replication in the Colicin E1 plasmid system by binding the primer-precursor transcript ColE1 RNA II. The binding interferes with the persistent RNA–DNA hybrid required for Ribonuclease H processing into an RNA primer. Its regulatory action therefore uses RNA recognition rather than translation into a repressor protein.[ref]
Control of ColE1 plasmid replication: the process of binding of RNA I to the primer transcript by J. Tomizawa. Abstract: RNA I–RNA II binding and inhibition of hybridization and primer formation.
The names mark opposing roles: ColE1 RNA II can proceed toward primer formation, while ColE1 RNA I can prevent that productive route. This is not equivalent to cutting an already completed DNA molecule. It changes whether a new replication round can start.
The 1984 binding experiments identified the interacting RNA product, providing physical evidence for the regulatory encounter. A change in plasmid copy number alone would be less specific evidence, since many later replication steps also affect that endpoint.[ref]
Control of ColE1 plasmid replication: the process of binding of RNA I to the primer transcript by J. Tomizawa. Binding demonstrated through identification of the RNA product.
For a qualitative competition example, consider a newly produced ColE1 RNA II transcript that can either form the productive DNA hybrid or be intercepted by ColE1 RNA I. Increasing the frequency of inhibitory encounters can lower the fraction entering the primer route even if the rate of precursor production is unchanged. The outcome depends on competing reaction rates and structures; it is not specified by a simple count of the two transcript names.
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