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Abstract:
Structures of a 10-subunit yeast RNA polymerase II have been derived from two
crystal forms at 2.8 and 3.1 angstrom resolution. Comparison of the structures
reveals a division of the polymerase into four mobile modules, including a
clamp, shown previously to swing over the active center. In the 2.8 angstrom
structure, the clamp is in an open state, allowing entry of straight promoter
DNA for the initiation of transcription. Three loops extending from the clamp
may play roles in RNA unwinding and DNA rewinding during transcription. A
2.8 angstrom difference Fourier map reveals two metal ions at the active site,
one persistently bound and the other possibly exchangeable during RNA synthesis.
The results also provide evidence for RNA exit in the vicinity of the
carboxyl-terminal repeat domain, coupling synthesis to RNA processing by
enzymes bound to this domain.
