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Helix–coil transition and conformational studies of protamine–DNA complexes

✍ Scribed by Sharon S. Yu; Hsueh Jei Li

Publisher
Wiley (John Wiley & Sons)
Year
1973
Tongue
English
Weight
561 KB
Volume
12
Category
Article
ISSN
0006-3525

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✦ Synopsis

Protamine-DNA complexes prepared by the method of direct and slow mixing in 2.5 x lO-4M EDTA, pH 8.0, have been studied by thermal denaturation and circular dichroism. The complexes show biphasic melting with T, at about 50°C corresponding to the melting of free DNA regions and T,' at about 92°C corresponding to the melting of protamine-bound regions. In protamine-bound regions there are 1.38 amino acid residues per nucleotide, indicating a nearly completely charge neutralization. T, is increased but T,' is not when the ionic strength of the buffer is raised. This also s u p ports a full charge neutralization in protamine-bound regions. The circular dichroism of the complexes can be decomposed into two components, ACO of free DNA regions in &form conformation and Aeb of protamine-bound regions in a characteristic conformation neither that of Bnor C-form but somewhere between them.

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