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Bending of the helical axis

Title		`STRUCTURE OF THE COMPLEX OF LAC REPRESSOR HEADPIECE AND AN 11 BASE-PAIR HALF-OPERATOR DETERMINED BY NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY AND RESTRAINED MOLECULAR DYNAMICS`
PDB code		`1LCC (PDB summary)`
NDB code		`1LCC (NDB atlas)`
Duplex length		`11 base pairs`
Protein		`Lactose operon repressor, Transcription factor, DNA binding domain: Lac I family`

Table 1. Bending parameters determined with the program ARC_FIT.
The curvilinear helical axis is calculated with CURVES, and bending of this axis is analysed with ARC_FIT. This program allows to fit a straight line, a plane, an arc, a kinked line, and a double kinked line to the helical axis. Good fits are indicated by low values of sigma². An arc is fitted if there are at least 7 bp. A kinked line requires at least 8 bp, and the double kinked line requires at least 13 bp. The geometrical parameters are given for all models fitted, but they characterize the shape of the helical axis only if the fit is good. See Help for further explanations.

Model	sigma² / Å²	Geometrical parameters
Plane	0.045
Straight line (x-axis)	1.565
Arc	0.216	Radius of curvature: r = 47 Å
Kinked line	0.207	Kink angle: alpha = 22° Lengths of straight segments: l₁ = 6 bp, l₂ = 5 bp