Helix-coil transitions in nucleoprotein: Computer-generated curves for independent melting of double-stranded regions with fixed ends
✍ Scribed by C. C. Chipev; D. Z. Staynov
- Book ID
- 102761667
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1978
- Tongue
- English
- Weight
- 665 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Helix-coil transitions in nucleoprotein a t low salt concentrations are known to be characterized by two phases of the process: independent melting of uncomplexed "naked" regions without rearrangement of proteins, followed, at higher temperatures, by melting of complexed DNA. Blocking at the ends of these regions increases their thermal stability and there is a shift of 10-20°C in t , of the melting profiles. In this study the basic assumption is that the loop entropy effect is mainly responsible for such stabilization. Calculations are made using conventional h-c transition theory for a system of independently melted segments with fixed ends. Segments are either homosize or have randomly distributed lengths. Calculated melting curves are used to obtain t,, and transition width-dependence on segment length (or average length when randomly distributed) and on the nucleation parameter u. Base-pair heterogeneity is taken into account by averaging over different base-pair distributions in the individual segments, using Gaussian distribution around the overall (G+C)-content. It is shown that this causes only an additional widening of the transition but no additional t , shift. Comparison is made with similar systems in the literature. The main conclusion drawn is that the treatment proposed may be useful for analysis of the lower temperature melting phase in nucleoprotein a t low counterion concentrations. It may be used as an independent method to reveal the features of nucleoprotein structure.