Coliphage N4 virion RNA polymerase (vRNAP), which is injected into the host upon infection, transcribes the phage early genes from promoters that have a 5-bp stem-3 nt loop hairpin structure. Here, we describe the 2.0-Å resolution x-ray crystal structure of N4 mini-vRNAP, a member of the T7-like, single-unit RNAP family and the minimal component having all RNAP functions of the fulllength vRNAP. The structure resembles a "fisted right hand" with Fingers, Palm and Thumb subdomains connected to an N-terminal domain. We established that the specificity loop extending from the Fingers along with W129 of the N-terminal domain play critical roles in hairpin-promoter recognition. A comparison with the structure of the T7 RNAP initiation complex reveals that the pathway of the DNA to the active site is blocked in the apo-form vRNAP, indicating that vRNAP must undergo a large-scale conformational change upon promoter DNA binding and explaining the highly restricted promoter specificity of vRNAP that is essential for phage early transcription.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Apr 1 2008|
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