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. 1974 Mar;71(3):593–597. doi: 10.1073/pnas.71.3.593

The lac Repressor Protein: Molecular Shape, Subunit Structure, and Proposed Model for Operator Interaction Based on Structural Studies of Microcrystals

Thomas A Steitz 1, Timothy J Richmond 1, David Wise 1, Donald Engelman 1
PMCID: PMC388057  PMID: 4595565

Abstract

Electron microscopic and powder x-ray diffraction studies of small crystals of the lac repressor protein provide evidence on its molecular shape and subunit structure which in turn suggests a possible mode of repressor—operator interaction. The crystals are probably orthorhombic space group P2221 with unit cell dimensions of a = 140, b = 91, c = 117 Å. This tetrameric protein appears rather asymmetric, having approximate molecular dimensions of 140 Å by 60 Å by 45 Å. The dumbbell shape of the projected molecular outline observed in the electron micrographs can be explained by assuming that the subunits are related by 222 symmetry and are placed at the corners of a plane rectangle. We propose a model for repressor—operator interaction in which the DNA binds to the repressor with its long axis aligned with that of the repressor and with its 2-fold axis coincident with a twofold axis of the repressor.

Keywords: electron microscopy, x-ray diffraction, protein-DNA interaction

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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