Predicted highly expressed and putative alien genes of Deinococcus radiodurans and implications for resistance to ionizing radiation damage

Predicted highly expressed (PHX) and putative alien genes determined by codon usages are characterized in the genome of Deinococcus radiodurans (strain R1). Deinococcus radiodurans (DEIRA) can survive very high doses of ionizing radiation that are lethal to virtually all other organisms. It has been argued that DEIRA is endowed with enhanced repair systems that provide protection and stability. However, predicted expression levels of DNA repair proteins with the exception of RecA tend to be low and do not distinguish DEIRA from other prokaryotes. In this paper, the capability of DEIRA to resist extreme doses of ionizing and UV radiation is attributed to an unusually high number of PHX chaperone/degradation, protease, and detoxification genes. Explicitly, compared with all current complete prokaryotic genomes, DEIRA contains the greatest number of PHX detoxification and protease proteins. Other sources of environmental protection against severe conditions of UV radiation, desiccation, and thermal effects for DEIRA are the several S-layer (surface structure) PHX proteins. The top PHX gene of DEIRA is the multifunctional tricarboxylic acid (TCA) gene aconitase, which, apart from its role in respiration, also alerts the cell to oxidative damage.

Thermotolerance and extended life-span conferred by single-gene mutations and induced by thermal stress.

We have discovered that three longevity mutants of the nematode Caenorhabditis elegans also exhibit increased intrinsic thermotolerance (Itt) as young adults. Mutation of the age-1 gene causes not only 65% longer life expectancy but also Itt. The Itt phenotype cosegregates with age-1. Long-lived spe-26 and daf-2 mutants also exhibit Itt. We investigated the relationship between increased thermotolerance and increased life-span by developing conditions for environmental induction of thermotolerance. Such pretreatments at sublethal temperatures induce significant increases in thermotolerance and small but statistically highly significant increases in life expectancy, consistent with a causal connection between these two traits. Thus, when an animal's resistance to stress is increased, by either genetic or environmental manipulation, we also observe an increase in life expectancy. These results suggest that ability to respond to stress limits the life expectancy of C. elegans and might do so in other metazoa as well.