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Bending of the helical axis

Title		`SOLUTION NMR STRUCTURE OF THE C-TERMINAL DOMAIN OF CHICKEN GATA-1 BOUND TO DNA, 34 STRUCTURES`
PDB code		`3GAT (PDB summary)`
NDB code		`3GAT (NDB atlas)`
Duplex length		`16 base pairs`
Protein		`Erythroid transcription factor GATA-1, Transcription factor, DNA binding domain: Cys4 zinc finger, divers`

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	0.056
Straight line (x-axis)	0.282
Arc	0.338	Radius of curvature: r = 912000000 Å
Kinked line	0.376	Kink angle: alpha = ill defined Lengths of straight segments: l₁ = 16 bp, l₂ = 0 bp
Double kinked line	0.130	Kink angles: alpha₁ = 12°, alpha₂ = 16° Twist angle: omega = 90° Lengths of straight segments: l₁ = 2 bp, l₂ = 12 bp, l₃ = 2 bp