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21.
Palindromy and the Location of Deletion Endpoints in Escherichia Coli 总被引:13,自引:3,他引:10
The contributions of direct and inverted repeats to deletion formation were studied by characterizing Ampr revertants of plasmids with a series of insertion mutations at a specific site in the pBR322 ampicillin resistance (amp) gene. The inserts at this site are palindromic, variable in length, and bracketed by 9- or 10-bp direct repeats of amp sequence. There is an additional direct repeat composed of 4 bp within the insert and 4 bp of adjoining amp sequence. DNA sequencing and colony hybridization of Ampr revertants showed that they contained either the parental amp sequence, implying deletion endpoints in the flanking 9- or 10-bp repeats, or a specific 1-bp substitution, implying endpoints in the 4-bp repeats. Although generally direct repeats seem to be used as deletion endpoints with a frequency proportional to their lengths, we found that with uninterrupted palindromes longer than 32 bp, the majority of deletions ended in the 4 bp, not the 9- or 10-bp repeats. This preferential use of the shorter direct repeats associated with palindromes is interpreted according to a DNA synthesis-error model in which hairpin structures formed by intrastrand pairing foster the slippage of nascent strands during DNA synthesis. 相似文献
22.
Bradyrhizobium japonicum Survival in and Soybean Inoculation with Fluid Gels 总被引:2,自引:0,他引:2 下载免费PDF全文
The utilization of gels, which are used for fluid drilling of seeds, as carriers of Bradyrhizobium japonicum for soybean (Glycine max (L.) Merr.) inoculation was studied. Gels of various chemical composition (magnesium silicate, potassium acrylate-acrylamide, grafted starch, and hydroxyethyl cellulose) were used, although the hydroxyethyl cellulose gels were more extensively investigated. Gel inocula were prepared by mixing gel powder with liquid cultures of B. japonicum (2% [wt/vol]). The population of B. japonicum USDA 110 did not change in each gel type during 8 days of incubation at 28°C. These fluid gels were prepared with late-exponential-growth-phase cells that were washed and suspended in physiological saline. Mid-exponential-growth-phase B. japonicum USDA 110, 123, and 138 grew in cellulose gels prepared with yeast extract-mannitol broth as well as or better than in yeast extract-mannitol broth alone for the first 10 days at 28°C. Populations in these cellulose gels after 35 days were as large as when the gels had originally been prepared, and survival occurred for at least 70 days. Soybeans grown in sand in the greenhouse had greater nodule numbers, nodule weights, and top weights with gel inoculants compared with a peat inoculant. In soil containing 103 indigenous B. japonicum per g of soil, inoculation resulted in increased soybean nodule numbers, nodule weights, and top weights, but only nodule numbers were greater with gel than with peat inoculation. The gel-treated seeds carried 102 to 103 more bacteria per seed (107 to 108) than did the peat-treated seeds. 相似文献
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24.
Effects of age and physical performance capacity on distribution and composition of high-density lipoprotein subfractions in men 总被引:1,自引:0,他引:1
Ingrid Frey Aloys Berg Manfred W. Baumstark Klaus-Günther Collatz Josef Keul 《European journal of applied physiology and occupational physiology》1990,60(6):441-444
The influences of age and maximal aerobic capacity (VO2max) on serum lipoproteins with special regard to the concentration, composition and distribution of high density lipoprotein (HDL) subfractions were investigated in 51 healthy males of different characteristics: younger than 35 years, untrained (n = 14, mean age 28.2 years, SD 6.0; VO2max, 47.9 ml.kg-1.min-1, SD 5.8) and trained (n = 11, mean age 27.9 years, SD 4.3; VO2max, 61.1 ml.kg-1.min-1, SD 5.1), older than 50 years untrained (n = 14, mean age 58.9 years, SD 5.9, VO2max, 29.3 ml.kg-1.min-1, SD 5.3) and trained (n = 12, mean age 59.3 years, SD 7.2, VO2max, 45.7 ml.kg-1.min-1, SD 7.7). The fasting-state serum concentrations of total cholesterol, tri-acylglycerol and lipoprotein-cholesterol were measured. The HDL-subfractions were separated by density (rho) gradient ultracentrifugation. Concentrations of cholesterol, cholesterylester, tri-acylglycerol, phospholipids, apolipoprotein (apo) A-I and A-II were measured in the subfractions HDL2b: rho = 1.063-1.100 g.ml-1; HDL2al: rho = 1.00-1.110 g.ml-1; HDL2a2: rho = 1.110-1.150 g.ml-1; HDL3: rho = 1.150-1.210 g.ml-1. Elderly untrained subjects showed increased serum concentrations of total-, very low- and low density lipoprotein-cholesterol and elevated tri-acylglycerol levels. The HDL-cholesterol concentration was decreased, due to reduced concentrations of HDL2-subfractions. Significant changes in the composition of HDL2-subfractions were found in elderly untrained subjects. The HDL2-subfractions had more protein, a decreased apoA-I:A-II ratio and less phospholipids in comparison to HDL2-subfractions from younger untrained and trained, and elderly trained subjects.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
25.
A fast method for the screening of a large number of immobilized dyes for the purification or binding of proteins called dye-ligand centrifugal affinity chromatography, is described. The ease and speed of this method is demonstrated by screening 65 immobilized dyes for the binding of purified goat IgG. Two immobilized dyes (Drimarene Blue K-R and Drimarene Rubine R/K-5BL) with a high affinity for goat IgG were found to bind specifically the Fc-fragment of the IgG. 相似文献
26.
S. Bissbort H. W. Hitzeroth D. P. du Wentzel C. W. Van den Berg H. Senff T. F. Wienker K. Bender 《Human genetics》1988,79(3):289-290
Summary We describe a new rare allele for esterase D (EsD) occurring in a Portuguese family with retinoblastoma in two generations. 相似文献
27.
Selection of DNA binding sites by regulatory proteins 总被引:15,自引:0,他引:15
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29.
The m gamma delta-1 element, a small gamma delta (Tn1000) derivative useful for plasmid mutagenesis, allele replacement and DNA sequencing. 总被引:9,自引:0,他引:9
C M Berg N B Vartak G Wang X Xu L Liu D J MacNeil K M Gewain L A Wiater D E Berg 《Gene》1992,113(1):9-16
Transposon gamma delta (Tn1000), a 6-kb member of the Tn3 family, is widely used for plasmid mutagenesis. A 1.8-kb derivative of gamma delta was constructed that contains the kan gene from Tn5 and the resolution (res) site from gamma delta cloned between 40-bp inverted repeats of gamma delta's delta (delta) end. This element, named m gamma delta-1, lacks the genes encoding transposase and resolvase, and therefore depends on its host to supply transposition and resolution functions. Thus, in strains lacking gamma delta, m gamma delta-1 will not transpose. The m gamma delta-1 element is shown to be useful for mutagenesis of plasmids, DNA sequencing, and allele replacement (in Streptomyces avermitilis). 相似文献
30.
Coen van den Berg Ferdinand A. Sibbing Jan W. M. Osse Wim Hoogenboezem 《Environmental Biology of Fishes》1992,33(1-2):105-124
Synopsis The filter feeding organ of cyprinid fishes is the branchial sieve, which consists of a mesh formed by gill rakers and tiny channels on the gill arches. In order to establish its possible role during growth we measured the following morphological gill raker parameters over a range of sizes in three cyprinid fishes, bream, white bream and roach: inter raker distance, bony raker length, raker width, cushion length and channel width. At any given standard length common bream has the largest inter raker distance, roach the lowest and white bream is intermediate. In the comb model of filter feeding the inter raker distance is considered to be a direct measure of the mesh size and retention ability (= minimal size of prey that can be retained) of a filter. For the three species under study there is a conflict between the comb model and experimental data on particle retention. Lammens et al. (1987) found that common bream has a large retention ability whereas roach and white bream have a much smaller one. A new model, the channel model (Hoogenboezem et al. 1991) has been developed for common bream; in this model the lateral gill rakers can regulate the mesh size of the medial channels on the other side of the gill slit. The present data indicate that this model is not appropriate for white bream and roach. At any given standard length white bream and roach only reach 70% of the raker length of common bream, which means that in this model the gill slits should to be very narrow during filter feeding. The gill rakers consist of a bony raker and a fleshy cushion. The bony rakers have a rather long needle-like part outside the cushion in bream, but not in white bream and roach which have blunt gill rakers. Blunt gill rakers are not suited to reduce the diameter of the medial channels. The comb model seems more appropriate for white bream and roach, but doubts about the validity of this simple model remain. The sum of the areas of the medial channels is an approximation of the area through which water flows in the filter. This channel area therefore gives an impression of the capacity or flow rate of the filter. With this capacity estimation and an estimation of energy consumption we calculated an energy ratio of filter feeding. The energy ratio decreases with increasing standard length with an exponent close to the expected exponent of -0.40. The energy ratio is highest in bream, intermediate in white bream and lowest in roach. 相似文献