Critical nuclear DNA size and distribution associated with S phase initiation

Using HeLa S-3 cells synchronized by selective detachment, in this paper we report a parallel study of nuclear morphology and autoradiography grain patterns between middle G₁ and middle S phases: Our results show two distinct [³H]-thymidine labeling patterns. The first “peripheral” labeling pattern has a characteristic nuclear size distribution, in contrast to the heterogeneous and varying size distributions of Feulgen-stained nuclei, and apparently is characteristic of very early S phase. The sizes of the second labeling pattern—homogeneous or inhomogeneous grain distribution throughout the nucleus—are equal or larger than the first and vary with S phase progression. Together, the corresponding nuclear sizes of the labeled nuclei represent the larger extreme of nuclear areas, and the labeling index closely parallels the fraction of nuclei with areas larger than the minimum size of the labeled nuclei. These results suggest a characteristic nuclear size (reflecting unique intranuclear DNA distribution) as a necessary, if not sufficient, requirement for S phase initiation. Parallel experimentation with rat liver cells—synchronized in vivo by partial hepatectomy and analyzed by thin section autoradiography—confirms the existence of a peripheral labeling pattern in both the very early part and the very late part of S phase, which reconciles our data with previous results and points to the fact that both initiation and termination sites for DNA replication are near the nuclear periphery.     

Community pattern analysis: A method for quantifying community mosaic structure

A method of quantifying community spatial patterns, community pattern analysis, is described. It is proposed that ordination analysis is used to obtain an integrated score for each quadrat from transect data. For the data presented here, separate ordinations were made of both floristic and environmental (soils) data. The ordination axis scores are then analysed using two or three-term local variance analysis to quantify the scales of community pattern. Correlation analyses allow the relationship between the vegetation and soils data (as represented by ordination axis scores), and other environmental data to be investigated at defined scales. The advantages of this method, that employs the joint application of conventional methods, are that it includes the influence of all species in the analysis, and that multiple uncorrelated scales of pattern within a community are identified.     

Morphologic characteristics of the Alaskan Eskimo dentition: IV. Cusp number and groove patterns of mandibular molars

Data on the permanent dentition of 63 coastal and 33 inland Alaskan Eskimos are presented. The number of cusps and groove pattern of the mandibular molars were recorded. Agenesis of the mandibular third molars was classified and the mesiodistal and buccolingual crown diameter was measured on the first and the second mandibular molars. The predominant pattern of the lower first molars was Y5, while for the second molar the dominating patterns were +5 and +4. In the lower third molar, +5 was found in the majority of cases. For M1 and M2, men showed a stronger tendency toward a conservative pattern than did women. In the case of M2, the inland population exhibited a more conservative trait than did the coastal population. No connection was seen between the groove pattern and agenesis of M3, however, a reduction in the mesiodistal crown diameter for the second molars was seen when the number of cusps is reduced from 5 to 4.     

Molecular epidemiology of plasmid patterns in Shigella dysenteriae type I obtained from an outbreak in West Bengal (India)

Abstract Multiple antibiotic-resistant Shigella dysenteriae type 1 isolates from a recent epidemic in West Bengal (India) showed identical plasmid patterns. All isolates were resistant to ampicillin (Am), chloramphenicol (Cm), tetracycline (Tc), streptomycin (Sm) and trimethoprim (Tp) and contained 6 plasmids, ranging from 2.5–120 kb. The Am resistance determinant was located on the 120 kb plasmid. This plasmid was unstable when the S. dysenteriae strains were grown above 37°C. The Bangladesh strains of S. dysenteriae type 1 showed identical plasmid patterns, except that many isolates were Am-sensitive and lacked the 120 kb plasmid. In strains from both Bangladesh and West Bengal, predominantly group-B plasmids conferred resistance to Cm and Tc. Comparisons of Eco R1 fragments generated from the total plasmid DNA content of each strain support the view that the plasmids present in the S. dysenteriae type 1 strains isolated from all recent epidemics in India and Bangladesh were identical.     

沙田柚染色体组型及Giemsa带型分析

本文以沙田柚为材料,对其染色体组型及带型进行了观察分析。组型分析:染色体数目2n=18,根据染色体的相对长度分成大小染色体两种类型,前者包括1、2、3、4和5对,后者为6、7、8和9对,根据臂比,9对染色体能够被分成中部着丝点和近中着丝点染色体两种类型。即第5、7,9对为亚中部着丝点,其余为中部着丝点,第6对染色体上有随体;Giemsa带型:除第二对染色体只显中间带外,其余都显着丝点带,并在3、4、8对染色体短臂上和2、3、1对染色体长臂上均显端带,第2、3,6对同源染色体之间的C带显示杂合性。     

关于植物核型分析的标准化问题

近年,我国的植物染色体研究工作,进展较快,并取得了显著的成绩。但在研究工作中仍存在一个迫切需要解决的问题,即核型分析的标准化问题。由于国际上尚无植物核型分析的共同标准,因此,有关染色体的统计、测量、命名、图表格式等等,各人所采用的方法和标准也不尽相同。这种状况,对核型资料的比较分析以及对研究结果的评价,都带来不便。有鉴于此,1984年8月在辽宁兴城召开的第一届全国植物染色体学术讨论会上,李懋学和陈瑞阳联名作了“关于植物核型分析的标准化问题”的报告,经过     

Protease activities in non-embryogenic and embryogenic carrot cell strains during callus growth and embryo formation

Embryogenic and non-embryogenic cell strains of Daucus carota L. were examined for their protease activity using a wide range of chromogenic synthetic peptides as substrates. High arginine-specific activity was present in all strains, but no protease activity "specific" for embryogenic or non-embryogenic strains could be detected with the substrates tested. The specific protease activity was 5–10 times higher in the non-embryogenic as compared to the embryogenic strain for most tested substrates, and this difference was not due to release of proteases in the latter. All strains showed a decrease in protease activity when cultured in media without 2,4-dichlorophenoxyacetic acid, but the embryos had high protease activity in comparison with the nondifferentiated cell aggregates. In the latter aggregates, hydrolyzing activity towards three of the substrates (H-D-Phe-Pip-Arg- p -nitroanilide, Suc-Ala-Pro-Phe- p -nitro-anilide and Bz-Phe-Val-Arg- p -nitroanilide) was absent, whereas the embryos were able to hydrolyze them.     

Nonrandomness of point mutation as reflected in nucleotide substitutions in pseudogenes and its evolutionary implications

Summary We have obtained a revised estimate of the pattern of point mutation by considering more pseudogene sequences. Compared with our previous estimate, it agrees better with expectations based on the double-strand structure of DNA. The revised pattern, like the previous one, indicates that mutation occurs nonrandomly among the four nucleotides. In particular, the proportion of transitional mutations (59%) is almost twice as high as the value (33%) expected under random mutation. The same high proportion of transitions is observed in synonymous substitutions in genes. The proportion of transitional changes observed among electrophoretic variants of human hemoglobin is about the same as that predicted by the revised pattern of mutation. We also show that nonrandom mutation increases, by about 15%, the proportion of synonymous mutations due to single-nucleotide changes in the codon table, and increases, from 10% to 50%, the rate of synonymous mutation in the seven genes studied. However, nonrandom mutation reduces (by about 10%) the proportion of polar changes among nonsynonymous mutations in a gene. As far as single-nucleotide changes (in the codon table) are concerned, nonrandom mutation only slightly favors relatively conservative amino acid interchanges, and has virtually no effect on the proportions of radical changes and nonsense mutations.     

碱性蛋白酶生产菌——地衣芽孢杆菌(B. licheniformis)的温和噬菌体

碱性蛋白酶生产菌——地衣芽孢杆菌经丝裂霉素C或紫外线处理,均可诱导释放噬菌体,电镜观察表明噬菌体头部外廓呈六边形,有不收缩的尾部(头部40nm×40nm,尾部107×5,7nm),噬菌体BLL1 DNA对限制酶Eco R Ⅰ,HindⅢ和Bam H Ⅰ敏感,分别切割成8,15,和9个片段,经电泳法测定。噬菌体DNA分子量约相当于23.4kb,根据解链温度计算出噬菌体的G+C含量约为31.2摩尔％,噬菌体提纯的外壳蛋白经SDS-聚丙烯酰胺凝胶电泳呈现5条主带,其分子量分别约为78000,72000,55000,39000,35000。     

Biotic regionalization and climatic controls in western North America

New methods of weather analysis accompanied by microhabitat ‘bioassays’ have been applied in several case studies to demonstrate effects of atmospheric processes on patterns of community composition and structure and potential species evolution. Average spatial and seasonal airmass dynamics which determine regional and elevational patterns of relative microhabitat favorability, were found to vary between a recent global warming trend (ca 1900 to 1940) and the subsequent global cooling trend (ca 1940 to 1970). These apparently systematic spatial and temporal shifts in weather were related to plant establishment patterns and community composition and structure. The proposed causal mechanisms function, in part, through regional shifts in microhabitat size. These effects are similar to larger scale, longer term shifts deduced from the late Quaternary fossil record. By modifying the spatial approach, month-to-month and year-to-year variability of weather has been examined for the last 130 years at individual points in southwestern North America. Three climatic regimes (the end of the Little Ice Age, the recent warming trend and the recent cooling trend) exhibited distinct year-to-year patterns of weather that can be related to the establishment of different kinds of plants (e.g., C₄ grasses versus C₃ shrubs). Oscillations between different temporal climatic regimes appear to promote the episodic establishment of different life forms, but not necessarily their local extinction. The two methods of weather analysis have been combined in a regional assessment of climatic controls of different biomes in space and time with a primary focus on the Chihuahuan desert. Natural ecotones between the Chihuahuan desert and neighboring biomes are clearly related to large scale airmass dynamics associated with seasonal oscillations in jetstream position. The weather patterns controlling ecotonal positions result from seasonal topographic influences on the general circulation of the atmosphere. The apparent stability of these patterns allows causal hypotheses of biogeographic dynamics and the evolution of physiological traits and life history characteristics.