Helix–Coil transition of plasmid dna by adiabatic differential scanning microcalorimetry

✍ Scribed by Y. Maeda; K. Takahashi; H. Yamaki; E. Ohtsubo

• Publisher: Wiley (John Wiley & Sons)
• Year: 1988
• Tongue: English
• Weight: 523 KB
• Volume: 27
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360271206

✦ Synopsis

Adiabatic differential scanning microcalorimetry, which provides curves of the heat capacity vs temperature, was carried out for the DNA of plasmid pJL3-TB5 (5277 base pairs in length). The calorimetry curve shows nine peaks ranging from 81 to 96°C in 1 X SSC buffer at a heating rate of 0.25'C, due to the stepwise helix-coil transition of the DNA along the molecular chain. The theoretical melting curve, which can be constructed by calculation from the entire nucleotide sequence of the plasmid DNA by the helix-coil transition theory, is then compared with the calorimetry curve. The two curves resemble each other remarkably well, particularly when a parameter for the methylated adenine residues at GATC sites by Dam methylase is used appropriately. This allows us to assign each peak in the calorimetry curve to the melting of the respective regions of the plasmid DNA sequence. The local stability of the helix-coil transition along the DNA chain is closely related to the functional regions coded by pJL3-TB5, such as genes, transcriptional promoters, and particular sites generated by recombination of two different sequences in vivo and in vitro.