Kefyalew Alemayehu and Damitie Kebede
Genomes of organisms growing at higher temperature would be subject to selection for a higher proportion of G+C than A+T, because of the increased number of hydrogen bonds between G and C than A and T on complementary strands. The thermopiles have mechanisms other than increasing G+C content for maintaining the double-stranded structure of their DNA at high temperatures. The existence of thermophile-specific enzymes, such as the reverse gyrase or selection for certain dinucleotides that may contribute to thermostability and adaptation mechanisms at the genome (DNA) level. The significant correlation between the G+C content of structural RNAs and growth temperature, and that the high G+C content is concentrated in the double-stranded stem regions of the molecule. This provides strong evidence for selection acting to increase the thermostability of these regions by changing the nucleotide composition and hence, adaptation mechanism at the transcriptome (RNA) level. When the protein structure is determined to a large extent by the primary amino-acid sequences, the consistent differences in amino-acid composition between the proteins of thermophiles and mesophiles can be observed and reported for individual genes and in whole-genome comparisons and hence Adaptations at the proteome (AA) level. The Central for the understanding thermotolerance and perhaps to the cellular role in acclimatization are the heat shock or stress proteins (HSPs). The requirement of HSPs for thermotolerance and the role of HSPs in protein folding, assembly, and transport support the hypothesis that the thermo-tolerant state is dependent on one or all of these HSPrelated functions, especially through the management of both denatured proteins and of partially synthesized protein fragments. In Physiological regulation of gene expression, receptor proteins and Intracellular mediators and second messengers play the basic role Reorganization of gene expression to benefit heart function during hibernation may be expected and the changes in protein products that result may, in fact, define the difference between the endurance of deep hypothermia by hibernating mammals and the lethal effects that equivalent hypothermia exposure has for most mammals, including man.
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