Identifying sites of simultaneous DNA replication in eukaryotes by N-methyl-N''-nitro-N-nitrosoguanidine multiple mutagenesis.

Summary N-methyl-N-nitro-N-nitrosoguanidine (NG) induces certain classes of multiple mutations in yeast at high frequency. By selecting for mutation at one locus (his4 or leu1) one frequently obtains double mutants where another mutation to temperature sensitivity has also been induced. This multiple mutagenesis exhibits a considerable specificity: for mutation at one particular locus there is a high chance that another mutation will be found in the same cell at one of a restricted number of other loci. For any given locus (e.g. his4) there is a spectrum of sites at which temperature-sensitivity mutations are coinduced. This spectrum differs for different loci, such that the spectrum of sites co-mutating with leul differs completely from that for sites co-mutating with his4. This NG-induced co-mutation is interpreted in terms of NG acting to enhance mutagenesis at sites of simultaneous DNA replication within the cell. The results so obtained indicate a very strict control over the order and timing of gene replication in Saccharomyces cerevisiae, and it is suggested that it is now possible to use NG double mutagenesis to try and locate origins of replication in yeast.     

Chromosomal analyses in vinyl chloride-exposed workers

Chromosomal morphology from cultured peripheral lymphocytes was studied in 81 men; 57 of the men were employed on plants manufacturing vinyl chloride or polyvinylchloride, 19 were on-site controls and 5 were off-site controls. There was a significant increase in chromosomal abnormalities in the exposed workers when compared with the controls. The greatest statistically significant increase in total B and total C cells occurred in autoclave operators, with smaller increases in other job categories. The increase in chromosomal aberrations was correlated with the length of exposure and with a history during the year prior to sampling (1973–1974) of exposure to excursion levels of vinyl chloride. Information on smoking habits was obtained 18 months after blood sampling and a positive correlation between these and total C cell abnormalities was found. There was no positive correlation with various other parameters (bilirubin, platelets, γ-glutamyltranspeptidase, alkaline phosphatase, alanine transaminase and aspartate transaminase). It was not possible to estimate which of the three parameters (smoking history, length of employment or exposure to excursion levels) was the most important.     

Detection and regulation of δ-aminolevulinic acid synthetase activity in rat skeletal muscle

The presence of δ-aminolevulinic acid synthetase (ALAS) in mitochondria obtained from rat skeletal muscles has been observed. Optimal conditions for the meausurement of this activity are described. The activity of skeletal muscle ALAS was investigated under conditions known to affect the activity of this enzyme in other tissues. ALAS activity in skeletal muscle mitochondria was decreased 55% by a 48-h fast. Treatment with dexamethasone did not reverse the effect of starvation on ALAS activity and did not change the activity in the fed controls. ALAS activity was decreased 56% in skeletal muscle mitochondria obtained from rats in which diabetes mellitus had been induced by streptozotocin. Administration of insulin to the diabetic animals partially reversed the effect of diabetes on skeletal muscle ALAS; however, administration of insulin to control animals caused a 21% decrease in skeletal muscle ALAS activity. By contrast, treatment with inducers of hepatic ALAS such as allylisopropylacetamide or 3,5-dicarbethoxy-1,4-dihydrocollidine had no effect on skeletal muscle ALAS. These results confirm our previous suggestion that ALAS activity is regulated in a tissue-specific manner.     

寡聚脱氧核苷酸d(G-C)_3的激光喇曼谱及其分析

用改进的固相磷酰三酯法合成了oligo-d(G-C)_3。以氩离子激光为激发光源,波长488nm.,在室温条件下,分别测定了纯化后的oligo-d(G-C)_3和其组分单体5’-dGMP和5’-dCMP的激光喇曼谱。观察到被测定的物质在300-2500cm~(-1)频率区间,各自都有其特征的谱形和喇曼峰。5’-dGMP和5’-dCMP谱中大多数特征峰在寡聚体的谱中消失,而在oligo-d(G-C)_3谱中出现了几处新的喇曼峰。经查证,峰832,851和899cm~(-1)系糖-磷酸主链的特征喇曼峰,另外几处峰与DNA的构象有关。实验结果表明oligo-d(G-C)_3在水溶液中(室温)主要以B-构象存在。     

通风结构林带背风面湍流相关特征初步分析

本文根据湍流统计理论和野外观测数据,详细分析了林带背风面湍流自相关、空间相关和湍流积分尺度特征。在林带背风面的林缘附近,由于湍流尺度较小,使湍流相关系数不紧密。这时的时间尺度在2—3s(1.5m)和3—8s(5m),而空间尺度为10—20m左右。在远离林带以后,林带的作用减弱,随着湍流尺度增大,导致湍流相关系数增大。这时的时间尺度在15—20s,空间尺度在70—80m范围内,且湍流自相关系数服从2/3的指数定律。     

东北主要造林树种的营养元素含量特征分析

 本文分析测定了东北地区9个主要针阔叶树种的营养元素含量和季节动态,并应用主成分分析和系统聚类分析方法,分析了各树种之间的营养元素相互关系。从而证明了N,P,Ca是植物重要的临界营养元素,Fe和Mn是表土中高度积累元素,树木对前者的吸收与土壤表土中含量有关,而对后者则表现相对的独立性和选择吸收能力。从营养元素的吸收与利用角度考虑,红松与胡桃楸混交,落叶松与水曲柳混交,硬阔叶树与软阔叶树混交,针阔叶树之间混交或白桦与其它各树种混交都是合理的。