We revisit the question of the  pitch angle of DNA , which has been suggested to be 45 deg . It is demonstrated that the pitch angle of DNA is well below 45 deg. For A-DNA it is approximately 28 deg., and for B-DNA  approximately 38 deg., in accord with the principle of optimal packing of tubular double helices .
The question of the value of the pitch angle of DNA is visited from the perspective of a geometrical analysis of transcription . It is suggested that for transcription to be possible, the pitch angle of B-DNA must be smaller than the angle of zero-twist. At the zero-twist angle the double helix is maximally rotated and its strain-twist coupling vanishes. A numerical estimate of the pitch angle for B-DNA based on differential geometry is compared with numbers obtained from existing empirical data. The crystallographic studies shows that the pitch angle is approximately 38 deg., less than the corresponding zero-twist angle of 41.8 deg., which is consistent with the suggested principle for transcription .
R
We revisit the
The
A
value of the
R
, which has been suggested to be 45 deg
is visited from the perspective of a geometrical analysis of transcription
R
demonstrated that
suggested that for transcription to be possible,
R
DNA is well below 45 deg. For A-DNA it is approximately 28 deg., and
B-DNA must be smaller than the angle of zero-twist. At the zero-twist angle the double helix is maximally rotated and its strain-twist coupling vanishes. A numerical estimate of the pitch angle
A
based on differential geometry is compared with numbers obtained from existing empirical data. The crystallographic studies shows that the pitch angle is
R
in accord with the principle of optimal packing of tubular double helices
less than the corresponding zero-twist angle of 41.8 deg., which is consistent with the suggested principle for transcription