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Abstract:
The trigger loop (TL) forms a conserved element in
the RNA polymerase active centre that functions in
the elongation phase of transcription. Here, we
show that the TL also functions in transcription initiation
and termination. Using recombinant variants
of RNA polymerase from Pyrococcus furiosus and a
reconstituted transcription system, we demonstrate
that the TL is essential for initial RNA synthesis until
a complete DNA–RNA hybrid is formed. The
archaeal TL is further important for transcription
fidelity during nucleotide incorporation, but not for
RNA cleavage during proofreading. A conserved
glutamine residue in the TL binds the 2’-OH group
of the nucleoside triphosphate (NTP) to discriminate
NTPs from dNTPs. The TL also prevents aberrant
transcription termination at non-terminator sites.
