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A ROLE FOR DAY AND NIGHT IN EVOLUTION BEN BLOOM* Help Wanted: Twenty men tenfeet tall, to work in primordialgoo eightfeet deep. The following is an amplification of a recently submitted abstract [i] in which homage was paid to the possibility that faulty proteins (defined as errant DNA translations) are not necessarily non-functional. That the synthesis offaulty proteins rarely, ifat all, influences the characteristics of succeeding generations seems highly probable. To the extent, however, that faulty proteins catalyze novel reactions which do influence, directly (errant duplicase) or indirectly, the accuracy of DNA duplication, succeeding generations will be affected. This thesis arose without prior knowledge of the investigations of Speyer demonstrating the existence of a mutagenic DNA polymerase [2].While the mechanism of action ofthis errant duplicase is not known, Speyer's suggestion that it may involve sequential information transfer from DNA to protein certainly deserves attention. The parallelism between errant DNA duplication and possible mutation phenomena appears pedestrian. Viewed in this context, ambiguous coding events, while endangering the survival of the individual, guarantee that the group makes a maximum effort at fitness evaluation. Insofar as amino acid-tRNA mismatching occurs, errantly charged tRNA will result, and faulty—possibly functional—proteins will be synthesized . Area, Frontali, and Tecce [3] have discovered that heat can determine whether ilu or val is to be the substrate for a purified ilu-tRNA synthetase (obtained from Bacillus stearothermophilus) in charging tRNAi(u. Also, i/w-tRNA synthetase preparations which do not show thr or ser-tRNA activities at 50° catalyze the formation ofser-tRNA and iAr-tRNA at 75o. * National Institute ofArthritis and Metabolic Diseases, National Institutes ofHealth, Bethesda, Maryland 20014. 1 wish to thank Dr. S. T. Algermissen for reviewing the geophysical data and Drs. P. Leder and Maxine F. Singer for the prepublication view oftheir article. 269 The effect oftemperature on the production ofambiguously charged, that is, mismatched, amino acid-tRNA's suggests a specific participation of heat in the evolutionary process. Indeed, the data indicate that at 80° every charged tRNA¿ju ofB. stearothermophilus will bear a val, and every nominal ilu containing protein will be faulty. The possibility that amino acid-tRNA mismatching is an essential feature ofthe evolutionary process cannot be ignored. A like role for heat affecting CODON-DECODON (anticodon) recognition can also be postulated [4]. To what extent did a day-night cycle contribute to the evolutionary process? The suggestion is offered that during some early phase of evolution , before the earth attained its present coolness, mutational events relatable to amino acid-tRNA mismatching occurred with great frequency during the warmth of day and that during the relative coolness ofnight the mutational survivors would accurately reproduce in numbers sufficient to contest their progenitors for environmental fitness. Indeed, temperatures above 700 [5] do not appear to be compatible with growth, possibly because of a high ratio of faulty to faultless protein synthesis. Whether a temperature of 700 is compatible with the preservation oflife does not appear to have been explored. A similar role for seasonal temperature variations, as well as day-night cyclic actions ofultraviolet, visible light, etc., is possible. To the extent that the above analysis is correct, the importance to the evolutionary process ofa warm body revolving relative to a heat source cannot be overemphasized. This thesis receives additional support from the fact that the difference in the temperature permitting matching of amino acids and tRNA's, 50°, and the maximum temperature at which growth can occur, 70o, is within the range of present-day diurnal temperature variations. It is of interest to consider the possibility that the upper permissible growth temperature is of evolutionary significance. It could be that it is relatable to the boiling point of water in io10 b.c. as determined by the atmospheric pressure of the era. A comment about the date io10 b.c. seems appropriate. It is intended to mean that tfie true number is closer to io10 B.c. than to io9 b.c. or 10" B.c. This is probably correct, for although the body of data indicates that the "age of the earth" is in the 4.3-4.7X io9 range [6,7], dating based...

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