RNAI is a non-coding RNA
Non-coding RNA
A non-coding RNA is a functional RNA molecule that is not translated into a protein. Less-frequently used synonyms are non-protein-coding RNA , non-messenger RNA and functional RNA . The term small RNA is often used for short bacterial ncRNAs...

 that is an antisense repressor of the replication of some E. coli plasmids, including ColE1. Plasmid replication is usually initiated by RNAII, which acts as a primer by binding to its template DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

. The complementary RNAI binds RNAII prohibiting it from its initiation role. The rate of degradation of RNAI is therefore a major factor in control of plasmid replication. This rate of degradation is aided by the pcnB (plasmid copy number B) gene product, which polyadenylates the 3' end of RNAI targeting it for degradation by PNPase.
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