B to Z transition in poly(dG-dC) modified with benzo(a)pyrene diol epoxides studied with polarized light spectroscopy
✍ Scribed by Magdalena Eriksson; Bengt Nordén; Bengt Jernström; Astrid Gräslund
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1990
- Tongue
- English
- Weight
- 1004 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
The NaC1-induced transition from B to Z conformation in poly( dG-dC) , covalently modified with benzo (a)pyrene diol epoxides (BPDE) , has been studied by use of flow linear dichroism ( L D ) , CD, and fluorescence spectroscopy. In contrast to unmodified poly( dG-dC), the BPDE-modified polynucleotide displays a B to Z conversion that is incomplete in 2.7 M NaCl. This and a number of other observations are found consistent with a locally retained BPDE perturbed B-like conformation in the vicinity of the BPDE adduct. In 2.7 M NaCl the polynucleotide orientation in flow is strongly reduced, which could indicate flexibility at the junctions between domains of BPDE perturbed B-like conformation and Z conformation. A virtually stable high-salt B form is found in 2.25 M NaCl at 0°C; its CD spectrum resembles that of the transient so-called B* form, which is observed at an early stage of the B to Z transition. Characteristic B to Z transition times were evaluated by taking this B*-form CD spectrum as the initial state spectrum. The kinetics of the B to Z transition, monitored by the CD signal at 287 nm, shows an increased transition rate with ( + ) -anti-BPDE modification whereas the ( -) -anti-and ( f ) -syn-BPDE adducts have retarding effects. The difference is discussed against the background of the different binding geometries of the BPDE isomer adducts.
'I Obtained by taking the B*-form CD as the initial spectrum.
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Calculations together with experimental obser-Dynam. 5, 1209-1219.