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111.
脱氨基被认为是引起细胞突变的主要因素,如果这些脱氨基的产物不被修复,将引起转换(transition)突变.为了理解DNA结构和其化学活性的关系,介绍一种新的灵敏的遗传学方法,它应用在DNA特定点的脱氨基速率的测定.这种方法基于M13mp2噬菌体内的1acZα基因中的CCC脯氨酸密码子的反转突变,即每个脱氨基事件表现为在白色菌斑背景中的一个蓝色菌斑,其灵敏度可达105 M13mp2 DNA分子中检验出一个脱氨基事件.此外,该法可以计算脱氨基动力学速率常数和反应活化能. 相似文献
112.
A nuclear genetic lesion affecting Saccharomyces cerevisiae mitochondrial translation is complemented by a homologous Bacillus gene. 总被引:1,自引:0,他引:1 下载免费PDF全文
S I Kim N Stange-Thomann O Martins K W Hong D Sll T D Fox 《Journal of bacteriology》1997,179(17):5625-5627
A novel Bacillus gene was isolated and characterized. It encodes a homolog of Saccharomyces cerevisiae Pet112p, a protein that has no characterized relative and is dispensable for cell viability but required for mitochondrial translation. Expression of the Bacillus protein in yeast, modified to ensure mitochondrial targeting, partially complemented the phenotype of the pet112-1 mutation, demonstrating a high degree of evolutionary conservation for this as yet unidentified component of translation. 相似文献
113.
The Mammalian Protein (rbet1) Homologous to Yeast Bet1p Is Primarily Associated with the Pre-Golgi Intermediate Compartment and Is Involved in Vesicular Transport from the Endoplasmic Reticulum to the Golgi Apparatus 总被引:7,自引:1,他引:6 下载免费PDF全文
Tao Zhang Siew Heng Wong Bor Luen Tang Yue Xu Frank Peter V. Nathan Subramaniam Wanjin Hong 《The Journal of cell biology》1997,139(5):1157-1168
Yeast Bet1p participates in vesicular transport from the endoplasmic reticulum to the Golgi apparatus and functions as a soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) associated with ER-derived vesicles. A mammalian protein (rbet1) homologous to Bet1p was recently identified, and it was concluded that rbet1 is associated with the Golgi apparatus based on the subcellular localization of transiently expressed epitope-tagged rbet1. In the present study using rabbit antibodies raised against the cytoplasmic domain of rbet1, we found that the majority of rbet1 is not associated with the Golgi apparatus as marked by the Golgi mannosidase II in normal rat kidney cells. Rather, rbet1 is predominantly associated with vesicular spotty structures that concentrate in the peri-Golgi region but are also present throughout the cytoplasm. These structures colocalize with the KDEL receptor and ERGIC-53, which are known to be enriched in the intermediate compartment. When the Golgi apparatus is fragmented by nocodazole treatment, a significant portion of rbet1 is not colocalized with structures marked by Golgi mannosidase II or the KDEL receptor. Association of rbet1 in cytoplasmic spotty structures is apparently not altered by preincubation of cells at 15°C. However, upon warming up from 15 to 37°C, rbet1 concentrates into the peri-Golgi region. Furthermore, rbet1 colocalizes with vesicular stomatitis virus G-protein en route from the ER to the Golgi. Antibodies against rbet1 inhibit in vitro transport of G-protein from the ER to the Golgi apparatus in a dose-dependent manner. This inhibition can be neutralized by preincubation of antibodies with recombinant rbet1. EGTA is known to inhibit ER-Golgi transport at a stage after vesicle docking but before the actual fusion event. Antibodies against rbet1 inhibit ER-Golgi transport only when they are added before the EGTA-sensitive stage. These results suggest that rbet1 may be involved in the docking process of ER- derived vesicles with the cis-Golgi membrane. 相似文献
114.
A Role for Cdk2 Kinase in Negatively Regulating DNA Replication during S Phase of the Cell Cycle 总被引:17,自引:4,他引:13 下载免费PDF全文
Using cell-free extracts made from Xenopus eggs, we show that cdk2-cyclin E and A kinases play an important role in negatively regulating DNA replication. Specifically, we demonstrate that the cdk2 kinase concentration surrounding chromatin in extracts increases 200-fold once the chromatin is assembled into nuclei. Further, we find that if the cdk2–cyclin E or A concentration in egg cytosol is increased 16-fold before the addition of sperm chromatin, the chromatin fails to initiate DNA replication once assembled into nuclei. This demonstrates that cdk2–cyclin E or A can negatively regulate DNA replication. With respect to how this negative regulation occurs, we show that high levels of cdk2–cyclin E do not block the association of the protein complex ORC with sperm chromatin but do prevent association of MCM3, a protein essential for replication. Importantly, we find that MCM3 that is prebound to chromatin does not dissociate when cdk2– cyclin E levels are increased. Taken together our results strongly suggest that during the embryonic cell cycle, the low concentrations of cdk2–cyclin E present in the cytosol after mitosis and before nuclear formation allow proteins essential for potentiating DNA replication to bind to chromatin, and that the high concentration of cdk2–cyclin E within nuclei prevents MCM from reassociating with chromatin after replication. This situation could serve, in part, to limit DNA replication to a single round per cell cycle. 相似文献
115.
The athermal bioeffects caused by nanosecond electromagnetic pulses with body cells was studied by using a broad band transverse EM-wave cell (BTEM CELL). The experimental system and preliminary mechanism analysis were presented. 相似文献
116.
不同光学异构体组成的氯氰菊酯对敏感及抗性家蝇的神经电生理学研究 总被引:3,自引:1,他引:2
采用敏感家蝇(Musca domestica vicina L.)及由5种不同光学异构体组成的氯氰菊酯选育的抗性家蝇中胸足离体标本,观测五种药剂对足感觉神经纤维冲动发放的影响。各种异构体组成的氯氰菊酯均可引起感觉神经纤维发放的增加,然后逐渐降低,直至完全阻断。以阻断时间和加药剂量为参数,求出神经敏感度。结果表明:五种药剂作用于敏感家蝇的神经敏感度与室内生物测定的LD50值(μg/头)无相关性,而与供试药剂中反α体与顺α体的比例有关,反α体所占比例越多的药物,神经敏感度越高。抗性家蝇的神经敏感度与敏感 家蝇相比大幅度下降,可以认为神经敏感度降低是家蝇对氯氰菊酯产生抗性的主要机制。抗性家蝇中,氯氰菊酯品系(RC1)的抗生水平最高,但它的神经敏感度较其它抗性品系也高,由此推测,RC1,的抗性机制与其它晶系有所不同。 相似文献
117.
异源八倍体小冰麦体细胞无性系的建立及其染色体变异 总被引:3,自引:0,他引:3
从5个异源八倍体小冰麦(Triticum -Agropyron)的叶片、幼穗及成熟胚诱导愈伤组织,建立体细胞无性系,获得大量再生植株。附加一个冰草染色体组的异源八倍体小冰麦杂种无性系中37.5% 表现变异,其中非整倍体植株变异较多,很多变异的再生植株形态与小麦近似,同时出现一定数量染色体重排、交换、易位、断裂、融合等变异。结果表明,通过杂种无性系变异进行染色体基因转化及遗传修饰是一条可行的途径。实验还观察了小冰麦愈伤组织分化过程中绿点的形成过程,首次提出两种类型绿点,即芽绿点和根绿点,并描述了两者的差异 相似文献
118.
干旱和湿润生境下辽东栎群体遗传结构及其适应意义的初步研究 总被引:3,自引:0,他引:3
应用同工酶分析方法,测定北京市东灵山区两个分别代表干旱和湿润生境的辽东栋(QuercusliaotungensisKoiz.)群体的遗传结构。共分析统计了13 个酶系统30 个位点。结果表明:辽东栎群体内部存在丰富的遗传变异(多态位点百分率为86.6% ,等位基因平均数为2.25)。两群体遗传结构的相似性程度很高(D= 0.029, GST= 0.048);但在个别位点上仍存在较大差异,这些差异的产生可能与对小生境的适应有关。对不同年龄段的初步分析结果显示,基因频率的动态变化可能有其适应意义 相似文献
119.
四个籼稻(Oryza sativa L.)品种幼苗经1℃黑暗或光照250 μm ol·m - 2·s- 1处理后,抗冷的“桂山矮选3”比不抗冷的“青华6 号”幼苗存活率高,其子代是以“桂山矮选3”为母本的比“青华6 号”为母本的存活率较高。抽穗期剑叶经光照低温处理12、24 和36 h 后,光合作用是“桂山矮选3”和以“桂山矮选3”为母本的子代比“青华6 号”和以“青华6 号”为母本的子代下降较少。呼吸作用是前者比后者在处理12 h 时有明显升高现象。荧光参数Fv/Fo和Fv/Fm比值在处理24 h 时前者比后者下降明显,但在常温下恢复则是前者比后者明显较快。自然低温(寒露风)对叶绿素荧光的影响亦有相似的规律。对水稻后代的抗冷性倾向于母本进行了讨论 相似文献
120.
Survival and Vigour of Lettuce (Lactuca sativa L.) and Sunflower (Helianthus annuus L.) Seeds Stored at Low and Very-low Moisture Contents 总被引:1,自引:0,他引:1
Seeds of lettuce (Lactuca sativa L.) and sunflower (Helianthusannuus L.) were stored hermetically at 35 °C with 11 differentmoisture contents between 1·3 and 6·9%, and between1·3 and 7·1% of fresh mass, respectively. Germinationand vigour (mean germination time, root length, seedling dryweight) were determined after storage for 0, 8, or 16 weeks(sunflower) or 0, 8, 16, or 48 weeks (lettuce) in these environmentsfollowed by various humidification treatments (to avoid imbibitioninjury). The range of seed storage moisture contents over whichdeterioration was minimized depended upon the criterion of deteriorationused, and varied somewhat between species. Comparison of theseranges for seeds stored for the longest durations showed thatfor some criteria seed performance was poorer (P < 0·05)at both the lowest and highest moisture contents investigatedthan at certain of the intermediate storage moisture contents(e.g, most rapid germination occurred in sunflower followingstorage at 2·2-4·7% moisture content), whereasfor other criteria all the drier storage moisture contents weresuperior to the more moist (e,g. greatest seedling growth occurredin sunflower following storage at 1·3-5·1% moisturecontent). But none of these results suggested that lettuce andsunflower seeds stored hermetically at 2·5-3·0%or 2·2-2·5% moisture content, respectively, wereless vigorous than at any other moisture content tested. Inboth species, these storage moisture contents are in equilibriumwith about 8-10% relative humidity (r.h.) at 20 °C, whichis similar to and indeed marginally less than the 10-13% r.h.recommended following earlier studies on the longevity of seedsin hermetic storage at much warmer temperatures. Thus, theseresults show no evidence that the optimum seed moisture contentfor storage increases with decrease in temperature, at leastover the range 35-65 °C, as has been suggested elsewhere.We conclude that the international recommendation for the long-termseed storage for genetic conservation at 5 ± 1% moisturecontent should not be revised upwardly, and that in situationswhere refrigeration cannot be provided storage at even lowermoisture contents is worthy of further investigation for thoseseeds in which desiccation at 20 °C to equilibrium at 10%r.h. results in moisture contents well below 5%.Copyright 1995,1999 Academic Press Helianthus annuus L., sunflower, Lactuca sativa L., lettuce, desiccation, seed storage, seed vigour 相似文献