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151.
The interpretation of ΔG (the free energy change for the reaction, globular conformation ? randomly coiled conformation, in the absence of denaturant), in terms of the free energies of transfer of various parts of the protein molecule from water to denaturant solution, is unsatisfactory because the latter are assumed to be identical to the transfer-free energies of similar groups attached to smaller model compounds. We have made empirical adjustments to transfer-free energy theory that make possible linear extrapolation of the free energy of denaturation of a protein from transition region to zero denaturant concentration. The modified theory, used to analyze the denaturation of proteins by guanidine hydrochloride and urea, allowed us to calculate reasonable values for Δα, the average change in accessibility to solvent of the component groups of protein. 相似文献
152.
The Evolution of Restricted Recombination and the Accumulation of Repeated DNA Sequences 总被引:19,自引:6,他引:13
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We suggest hypotheses to account for two major features of chromosomal organization in higher eukaryotes. The first of these is the general restriction of crossing over in the neighborhood of centromeres and telomeres. We propose that this is a consequence of selection for reduced rates of unequal exchange between repeated DNA sequences for which the copy number is subject to stabilizing selection: microtubule binding sites, in the case of centromeres, and the short repeated sequences needed for terminal replication of a linear DNA molecule, in the case of telomeres. An association between proximal crossing over and nondisjunction would also favor the restriction of crossing over near the centromere. The second feature is the association between highly repeated DNA sequences of no obvious functional significance and regions of restricted crossing over. We show that highly repeated sequences are likely to persist longest (over evolutionary time) when crossing over is infrequent. This is because unequal exchange among repeated sequences generates single copy sequences, and a population that becomes fixed for a single copy sequence by drift remains in this state indefinitely (in the absence of gene amplification processes). Increased rates of exchange thus speed up the process of stochastic loss of repeated sequences. 相似文献
153.
Keith Condon Douglas K. Charles James M. Cheverud Jane E. Buikstra 《American journal of physical anthropology》1986,71(3):321-330
The cementum annulation aging technique was evaluated in a sample of 80 clinically extracted premolars (age range 11–70 years). Demineralized thin sections (7μm) stained with hematoxylin were used. The correlation (r) between age and adjusted count (number of annulations added to age of tooth eruption) was 0.78 for the entire sample (N = 73) and 0.86 for a subsample in which teeth with periodontal disease were excluded (N = 55). Standard error of the estimates ranged from 4.7 to 9.7 years depending on sex and health status of the tooth. The technique provided significantly better estimates for females than for males. The overall inaccuracy (mean absolute error) of the technique was 6.0 years, with a bias (mean error) of 0.26 years. Reduced major axis regression of adjusted count on age produced a slope of 0.797 for the entire sample and 0.889 for the nonperiodontal disease subsample. These slopes are consistent with a hypothesis of annual deposition of cementum rings given a decrease in cementogenesis with increasing age. 相似文献
154.
Comparative Study of Action of Cell Wall Proteinases from Various Strains of Streptococcus cremoris on Bovine αs1-, β-, and κ-Casein
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Servaas Visser Fred A. Exterkate Charles J. Slangen Gerrie J. C. M. de Veer 《Applied microbiology》1986,52(5):1162-1166
Partially purified cell wall proteinases of eight strains of Streptococcus cremoris were compared in their action on bovine αs1-, β-, and κ-casein, as visualized by starch gel electrophoresis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and thin-layer chromatography. Characteristic degradation profiles could be distinguished, from which the occurrence of two proteinases, represented by strain HP and strain AM1, was concluded. The action of the HP-type proteinase P1 (also detectable in strains Wg2, C13, and TR) was established by electrophoretic methods to be directed preferentially towards β-casein. The AM1-type proteinase PIII (also detectable in strain SK11) was also able to degrade β-casein, but at the same time split αs1- and κ-casein more extensively than did PI. Strain FD27 exhibited mainly PI activity but also detectable PIII degradation characteristics. The cell wall proteinase preparation of strain E8 showed low PI as well as low PIII activity. All proteinase preparations produced from κ-casein positively charged degradation products with electrophoretic mobilities similar to those of degradation products released by the action of the milk-clotting enzyme chymosin. The differences between PI and PIII in mode of action, as detected by gel electrophoresis and thin-layer chromatography, were reflected by the courses of the initial degradation of methyl-14C-labeled β-casein and by the effect of αs1- plus κ-casein on these degradations. The results are discussed in the light of previous comparative studies of cell wall proteinases in strains of S. cremoris and with respect to the growth of this organism in milk. 相似文献
155.
Alfredo Munoz-Rivas Charles A. Specht Bruce J. Drummond Eunice Froeliger Charles P. Novotny Robert C. Ullrich 《Molecular & general genetics : MGG》1986,205(1):103-106
Summary Protoplasts of aSchizophyllum commune tryptophan auxotroph (trp1), deficient in indole-3-glycerol phosphate synthetase (IGPS), were transformed to trp+ with plasmid DNA containing the SchizophyllumTRP1 sequence. Efficiencies up to 30 transformants per microgram of plasmid DNA were obtained. Southern blots reveal that the
transforming DNA is integrated in chromosomal DNA. The trp+ phenotype of transformants is stable in meiosis and mitosis. Transformants possess IGPS activity comparable to wild-type
cells. 相似文献
156.
Takeshi Murakami Hiroyuki Anzai Satoshi Imai Atsuyuki Satoh Kozo Nagaoka Charles J. Thompson 《Molecular & general genetics : MGG》1986,205(1):42-53
Summary We have isolated and studied the organization ofStreptomyces hygroscopicus genes responsible for the biosynthesis of the antibiotic herbicide bialaphos. Bialaphos production genes were cloned from
genomic DNA using a plasmid vector (pIJ702). Three plasmids were isolated which restored productivity toS. hygroscopicus mutants blocked at different steps of the biosynthetic pathway. Subcloning experiments using other nonproducing mutants showed
that four additional bialaphos production genes were also contained on these plasmids. A gene conferring resistance to bialaphos,
which was independently cloned using the plasmid vector pIJ61, and an antibiotic-sensitive host (S. lividans), was also linked to the production genes. Cosmids were isolated which defined the location of these genes in a 16 kb cluster. 相似文献
157.
Cloning and expression of a tylosin resistance gene from a tylosin-producing strain of Streptomyces fradiae 总被引:1,自引:0,他引:1
Virginia A. Birmingham Karen L. Cox Jeffrey L. Larson Scott E. Fishman Charles L. Hershberger Eugene T. Seno 《Molecular & general genetics : MGG》1986,204(3):532-539
Summary A gene conferring high-level resistance to tylosin in Streptomyces lividans and Streptomyces griseofuscus was cloned from a tylosin-producing strain of Streptomyces fradiae. The tylosin-resistance (Tylr) gene (tlrA) was isolated on five overlapping DNA fragments which contained a common 2.6 Kb KpnI fragment. The KpnI fragment contained all of the information required for the expression of the Tylr phenotype in S. lividans and S. griseofuscus. Southern hybridization indicated that the sequence conferring tylosin resistance was present on the same 5 kb SalI fragment in genomic DNA from S. fradiae and several tylosin-sensitive (Tyls) mutants. The cloned tlrA gene failed to restore tylosin resistance in two Tyls mutants derived by protoplast formation and regeneration, and it restored partial resistance in a Tyls mutant obtained by N-methyl-N-nitro-N-nitrosoguanidine (MNNG) mutagenesis. The tlrA gene conferred resistance to tylosin, carbomycin, niddamycin, vernamycin-B and, to some degree, lincomycin in S. griseofuscus, but it had no effect on sensitivity to streptomycin or spectinomycin, suggesting that the cloned gene is an MLS (macrolide, lincosamide, streptogramin-B)-resistance gene. Twenty-eight kb of S. fradiae DNA surrounding the tlrA gene was isolated from a genomic library in bacteriophage Charon 4. Introduction of these DNA sequence into S. fradiae mutants blocked at different steps in tylosin biosynthesis failed to restore tylosin production, suggesting that the cloned Tylr gene is not closely linked to tylosin biosynthetic genes. 相似文献
158.
Summary The effects of food on breeding success and behavior of the red-winged blackbird (Icteridae: Agelaius phoeniceus) were investigated during 3 successive breeding seasons. In the second season, a 4-week pulse of abundant food in the form of a periodical cicada emergence (Homoptera: Cicadidae: Magicicada spp.) occurred in the forest adjacent to the marsh where the birds were breeding.During the cicada period, the bird population showed: 1) an increase in foraging trips to the forest and a decrease in trips per h, 2) increased biomass of nestlings, 3) increased nestling survival caused by decreased starvation, 4) increased fledging success, and 5) bimodal weight distributions of older nestlings (reflective of the sexual dimorphism in this species). These data suggest the temporary removal of food limitations on the breeding population when the pulse of food was available. 相似文献
159.
Fujioka Shozo; Sakurai Akira; Yamaguchi Isomaro; Murofushi Noboru; Takahashi Nobutaka; Kaihara Sumiko; Takimoto Atsushi; Cleland Charles F. 《Plant & cell physiology》1986,27(7):1297-1307
The occurrence and endogenous level of various plant hormoneswere measured for the short-day plants Lemna paucicostata 151and 381 and the long-day plant Lemna gibba G3 to determine whetherany of them are involved in the photoperiodic control of flowering.ABA, IAA, GA1, GA29, GA34, GA53, trans- and cis-zeatin, trans-and cis-ribosyl zeatin, N6-(2-isopentenyl) adenine and N6-(2-isopentenyl)adenosine were definitely detected in each species, while GA4was only detected in L. gibba G3 and GA20 was only detectedin L. paucicostata 151. The endogenous levels of ABA and IAAwere in the range of 17 ng/g fr wt and were not significantlydifferent in vegetative and flowering plants. The endogenousgibberellin levels were generally higher in Lemna grown underlong-day rather than short-day conditions. The endogenous cytokininlevels were almost the same in both flowering and vegetativeplants of L. paucicostata 151 and 381. In L. gibba G3, however,the level of cis-ribosyl zeatin, N6-(2-isopentenyl) adenineand N6-(2-sopentenyl) adenosine were higher in vegetative thanin flowering plants. These results indicate that there is not necessarily a directrelation between endogenous plant hormone levels and flowering,and that the chemical basis for the photoperiodic control offlowering cannot be explained solely by changes in hormone levels.The possibility remains, however, that one or more of the planthormones has some influence of secondary importance on the floweringprocess in Lemna. (Received January 29, 1986; Accepted July 12, 1986) 相似文献
160.
The long-day plant Lemna gibba G3 flowers normally in E medium(Hoagland-type medium plus 30 µM EDTA) but in 0.5 H mediumthere is no flowering. Ammonium is present in 0.5 H medium andis known to inhibit flowering in L. gibba G3, but even in NH4+-free0.5 H medium there is virtually no flowering under continuouslight. Increasing the phosphate concentration of the NH4+-free0.5 H medium from 1.15 ITIM to 12 or 16 mM results in substantialflowering. Decreasing the EDTA concentration from 850 µIMto 250 µM, or raising the nitrate concentration from 4mM to 12 mM, results in only a small increase in flowering.If the decrease in EDTA and increase in nitrate are combinedwith the increase in phosphate, however, the flowering responseis nearly as good as that obtained using E medium. Thus, withthese three changes the inhibitory effect of NH4+free 0.5 Hmedium for flowering in L. gibba G3 is almost completely reversed In the above studies flowering was not limited by daylength.When plants were grown on E medium under an 11 hour daylengthwhere flowering is limited by daylength, decreasing the phosphateconcentration in the medium reduced flowering, but increasingthe phosphate concentration in the medium did not stimulateflowering. Thus, when flowering is limited by daylength, highphosphate will not cause flowering, but a certain level of phosphateappears to be necessary for the expression of photoinductionunder long days. (Received January 14, 1986; Accepted June 24, 1986) 相似文献