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キーワード:
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要旨:
Structures of multisubunit RNA polymerases strongly
differ from the many known structures of single subunit
DNA and RNA polymerases. However, in functional
complexes of these diverse enzymes, nucleic acids take
a similar course through the active center. This finding
allows superposition of diverse polymerases and reveals
features that are functionally equivalent. The entering
DNA duplex is bent by almost 908 with respect to the
exiting template–product duplex. At the point of bending,
a dramatic twist between subsequent DNA template
bases aligns the ‘‘coding‘‘ base with the binding site for
the incoming nucleoside triphosphate (NTP). The NTP
enters through an opening that is found in all polymerases,
and, in most cases, binds between an a-helix
and two catalytic metal ions. Subsequent phosphodiester
bond formation adds a new base pair to the exiting
template–product duplex, which is always bound from
the minor groove side. All polymerases may undergo
‘‘induced fit’’ upon nucleic acid binding, but the underlying
conformational changes differ.
