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Bending of the helical axis

Title		`STRUCTURE OF THE REPLICATING COMPLEX OF A POL ALPHA FAMILY DNA POLYMERASE`
PDB code		`1IG9 (PDB summary)`
NDB code		`PD0212 (NDB atlas)`
Duplex length		`13 base pairs`
Protein		`Pol alpha, Polymerase`

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	0.025
Straight line (x-axis)	0.455
Arc	0.216	Radius of curvature: r = 148 Å
Kinked line	0.106	Kink angle: alpha = 12° Lengths of straight segments: l₁ = 4 bp, l₂ = 9 bp
Double kinked line	0.110	Kink angles: alpha₁ = 13°, alpha₂ = 6° Twist angle: omega = 151° Lengths of straight segments: l₁ = 5 bp, l₂ = 4 bp, l₃ = 4 bp