Left handed DNA in synthetic and topologically constrained form V DNA and its implications in protein recognition

Shouche, Y. S. ; Latha, P. K. ; Ramesh, N. ; Majumder, K. ; Mandyan, V. ; Brahmachari, Samir K. (1985) Left handed DNA in synthetic and topologically constrained form V DNA and its implications in protein recognition Journal of Biosciences, 8 (3-4). pp. 563-578. ISSN 0250-5991

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Official URL: http://www.ias.ac.in/jarch/jbiosci/8/563-578.pdf

Related URL: http://dx.doi.org/10.1007/BF02702756


We have investigated structural transitions in Poly(dG-dC) and Poly(dG-Me5dC) in order to understand the exact role of cations in stabilizing left-handed helical structures in specific sequences and the biological role, if any, of these structures. From a novel temperature dependent Z⇌B transition it has been shown that a minor fluctuation in Na+ concentration at ambient temperature can bring about B to Z transition. For the first time, we have observed a novel Z⇌B⇌Zuble transition in poly(dG-Me5dC) as the Na+ concentration is gradually increased. This suggests that a minor fluctuation in Na+ concentration in conjunction with methylation may transform small stretches of CG sequences from one conformational state to another. These stretches could probably serve as sites for regulation. Supercoiled form V DNA reconstituted from pBR322 and pβG plasmids have been studied as model systems, in order to understand the nature and role of left-handed helical conformation in natural sequences. A large portion of DNA in form V, obtained by reannealing the two complementary singlestranded circles is forced to adopt left-handed double helical structure due to topological constraints (Lk=0). Binding studies with Z-DNA specific antibody and spectroscopic studies confirm the presence of left-handed Z-structure in the pβG and pβR322 form V DNA. Cobalt hexamine chloride, which induces Z-form in Poly(dG-dC) stabilizes the Z-conformation in form V DNA even in the non-alternating purine-pyrimidine sequences. A reverse effect is observed with ethidium bromide. Interestingly, both topoisomerase I and II (from wheat germ) act effectively on form V DNA to give rise to a species having an electrophoretic mobility on agarose gel similar to that of open circular (form II) DNA. Whether this molecule is formed as a result of the left-handed helical segments of form V DNA undergoing a transition to the right-handed B-form during the topoisomerase action remains to be solved.

Item Type:Article
Source:Copyright of this article belongs to Indian Academy of Sciences.
Keywords:Poly(dG-Me5C); Z⇌B⇌Z; Form V; Topoisomerase
ID Code:44512
Deposited On:22 Jun 2011 08:38
Last Modified:18 May 2016 01:08

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