DNA POLYMORPHISM UNDER THE INFLUENCE OF LOW PH AND LOW-TEMPERATURE

The polymorphic behaviour on the conformation of a alternating GC poly mer and its methylated analogue has been studied under the influence o f low pH, low temperature and low ionic strength from the measurements of W-absorption and circular dichroic spectroscopy. Studies indicate that both the polymers isomerize to a stable left handed type conforma tions. The duplex nature of these conformations were inferred from the rmal denaturation curves and the temperature dependence of the CD spec tra. In natural DNA, the influence of low pH and low temperature also shows a defined conformational change, characterized by two positive C D bands. This conformational status is achieved in all DNAs irrespecti ve of base composition or sequence of base pairs. Further evidence to this altered polymorphic state of natural DNAs is inferred from ethidi um binding study.