Antitermination factors
Antitermination is the prokaryotic cell's aid to fix premature termination of RNA synthesis during the transcription of RNA.
It occurs when the RNA polymerase ignores the termination signal,and
continues elongating its transcript until a second signal is reached and
it provides a mechanism whereby one or more genes at the end of an
operon can be switched either on or off, depending on the polymerase
either recognizing or not recognizing the termination signal.
Antitermination is used by some phages to regulate progression from
one stage of gene expression to the next. The lambda gene N, codes for
an antitermination protein (pN) that is necessary to allow RNA
polymerase to read through the terminators located at the ends of the
immediate early genes. Another antitermination protein, pQ, is required
later in phage infection. pN and pQ act on RNA polymerase as it passes
specific sites. These sites are located at different relative positions
in their respective transcription units.
UUUUUUU
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3125153/
https://www.ncbi.nlm.nih.gov/pubmed/10230402/
In bacteria, an intrinsic transcription termination signal appears in
RNA as a hairpin followed by approximately eight uridines (U stretch) at
the 3' terminus. This signal leads to rapid dissociation of the ternary
elongation complex (TEC) into RNA, DNA, and an RNA polymerase. We
demonstrate that the hairpin inactivates and then destabilizes TEC by
weakening interactions in the RNA-DNA hybrid-binding site and the
RNA-binding site that hold TEC together. Formation of the hairpin is
restricted to the moment when TEC reaches the point of termination and
depends upon melting of four to five hybrid base pairs that follow the
hairpin's stem. The U stretch-induced pausing at the point of
termination is crucial, providing additional time for hairpin formation.
These results explain the mechanism of termination and aid in
understanding of how cellular factors modulate this process.
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