光复活对紫外线照射大肠杆菌后突变率的影响

通过改变UV照射时间、照射后的操作速度、光复活时的温度、时间和光强度,以光复活和暗处理后细胞存活数的比值为依据,研究了不同条件下E．coli受UV照射后的光复活效应。并以E．coli对5μg/ml链霉素抗性突变率为指标,比较了不同剂量UV照射后光复活和暗处理对E．coli突变率的影响。结果表明：光复活效应在温度10℃时最明显,且与照射时间、照射后的操作速度、光复活时间和光强度成正相关;在中、低剂量UV照射后,暗处理较光复活后E．coli对链霉素抗性突变率明显高,而在高剂量下,光复活则显著高于暗处理后的突变率。     

Ultraviolet Inactivation and Photoreactivation in Synchronized Chlorella

Synchronous cultures of Chlorella pyrenoidosa have been used in studies of the action of UV-irradiation during different stages in the life cycle on cell division capacity. These experiments show that there is a considerably higher sensitivity to UV-irradiation during the first hours of the life cycle. The variations in photoreactivating capacity of UV-damaged cells during a life cycle have been investigated. The results from these investigations show that the photoreactivating capacity varies and that it is higher in young daughter cells (autospores) and 12–15 hour cells. These variations can be due to variations in the activity of the photoreactivating enzyme during the life cycle.     

Spontaneous Mutation Rate of Modifiers of Metabolism in Drosophila

A rigorous test of our understanding of evolutionary quantitative genetics would be to predict accurately the equilibrium distribution of a character from empirical estimates of the relevant parameters in a mutation-selection-drift balance model. an aspect of this problem that is amenable to experimental analysis is the distribution of the effects of new mutations. This study quantifies the divergence among 200 lines of Drosophila melanogaster as they accumulated mutations on the second chromosome and estimates the rate of increase of variation and covariation in metabolic characters. Amounts of stored triacylglycerol and glycogen and the activities of a series of 12 metabolic enzymes were assayed in a subset of lines at generations 0, 11, 22, 33 and 44. Analyses of the rate of increase in the among-line variance in each trait allowed estimation of V(m)/V(e), the ratio of among-line variance added per generation to the environmental variance. Values of V(m)/V(e) for the second chromosome ranged from 0.0004 to 0.0289 per generation. Six of the 16 characters showed significant departure from a normal distribution, and several lines exhibited large changes in more than one character. The covariance of pairs of traits also was partitioned into a within-line component (environmental covariance, Cov(e)) and an among-line component (mutational covariance, Cov(m)). Both variances and covariance among lines increased over time, as assessed by linear regression, whereas environmental covariance showed no such trend. Results indicate that the quantitative genetic parameters describing the variation in metabolic traits are similar to those of other continuous characters.     

Ultraviolet Light Inactivation and Photoreactivation of AS-1 Cyanophage in Anacystis nidulans

Black light effected photorecovery of AS-1 cyanophage and wild-type cells. However, only partial photoreactivation of AS-1 was observed in a partially photoreactivable mutant of Anacystis nidulans.     

The Quantitative Interrelationships between Ion Fluxes, Cell Swelling, and Radiation Dose in Ultraviolet Hemolysis

Following treatment with ultraviolet radiation, human red cells leak cations at accelerated rates which depend on the radiation dose. With one exception (initial Na efflux), these accelerated cation fluxes fit the Ussing flux-ratio criterion for passive diffusion. Na efflux is transiently high, but with time falls to the value expected on the basis of the other cation fluxes. An equation based on the hypothesis of colloid osmotic hemolysis satisfactorily predicts the rate of cell swelling as a result of these ion movements.     

Specificity in the Photoreactivation of Premutational Damage Induced in Neurospora crassa by Ultraviolet

Summary Photoreactivation of the events which lead to ultraviolet-induced reversion of sixteen mutants has been studied. Reversion of one mutant, the inositol allele 37401, is photoreactivated far less than lethal damage. Reversion of the remaining 15 mutants, alleles at three different loci, is photoreactivated to the same extent as lethal damage. Various explanations of this finding are considered and the implications of repair specificity in modifying mutagen specificity are discussed briefly.