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11.
The T1 pac site has been cloned into a plasmid vector. This recombinant plasmid was tested for T1-mediated transduction efficiency in comparison with a plasmid containing the phage lambda T1-pac-like site esp-lambda, plasmids containing T1 sequences other than the pac site, and plasmids containing neither T1 sequences nor known pac sites. The data obtained indicate that there are at least two distinct mechanisms of T1-mediated plasmid transduction. One requires the presence of any T1 sequence on the plasmid and probably takes place via cointegrate formation with the homologous region of an infecting T1 genome. The other is specifically dependent on the presence of a pac site on the plasmid. Plasmids are packaged as head-to-tail multimers that have one heterogeneous molecular end and the other terminated at pac, and the direction of packaging with respect to the pac site is the same for plasmids as for T1. Possible roles of pac in plasmid packaging and their implications with regard to the packaging of phage DNA are discussed. 相似文献
12.
Mutant of Salmonella typhimurium LT2 deficient in DNA adenine methylation. 总被引:2,自引:0,他引:2
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A mutant of Salmonella typhimurium LT2 deficient in methylation of the adenine residues in the sequence 5'-GATC-3' was isolated. The mutation (dam-1) was linked to the cysG locus, and the properties of the mutant were similar to those of Escherichia coli dam mutants. Reversion of the hisC3076 frameshift marker by 9-aminoacridine was substantially enhanced by the dam-1 mutation, implying a direct role for adenine methylation in the prevention of frameshift mutation induction. 相似文献
13.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
14.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
15.
Terry Ritchie Sheila A. Scully Jean de Vellis Ernest P. Noble 《Neurochemical research》1986,11(3):383-392
The enzymatic activities in post-mortem rat brain kept at 4°C and at 25°C were determined for a number of enzymes localized in specific cell types in the central nervous system. Choline acetyltransferase (CAT), glycerol-3-phosphate dehydrogenase (GPDH), glutamine synthetase (GS), lactate dehydrogenase (LDH) and 2,3-cyclic nucleotide phosphohydrolase (CNPase) were found to be very stable at both 4°C and 25°C with only slight, if any, losses of activity being seen even at periods as long as 72 hr. Glutamic acid decarboxylase (GAD) activity was less stable than that of the other enzymes. In brains kept at 4°C GAD activity was stable out to 24 hr after which it began to decline rapidly to 65% of control at 72 hr. In brains kept at 25°C, GAD activity was stable for 6–8 hr and then began to steadily decline to 58% of control at 24 hr and 29% of control at 72 hr. Assuming that these enzymes have similar stabilities in post-mortem human brain, the effect of post-mortem delay in processing tissues may be of lesser significance than other factors with regard to the measured enzyme activities in human brain samples. 相似文献
16.
E W Ainscough A M Brodie S J McLachlan V S Ritchie 《Journal of inorganic biochemistry》1983,18(2):103-112
The interaction of Cu(II) with human lactoferrin has been studied as a function of pH, using electronic and electron spin resonance spectroscopy. Specific Cu(II) binding, with bicarbonate as the co-anion, occurs over the pH range 6 to 9. In the presence of a fiftyfold molar excess of oxalate, a monocopper(II) lactoferrin oxalate complex forms when the Cu(II) to protein is 1:1. If this ratio is increased to 2:1, a hybrid complex forms, in which the second copper utilizes bicarbonate as the co-anion, thus demonstrating, as for serum transferrin, a difference in the anion binding sites. The quenching of the intrinsic fluorescence of apolactoferrin is significantly less in the presence of oxalate than bicarbonate. The interaction of Cu(II) with apolactoferrin in the presence of the malonate, glycolate, thioglycolate, glycinate, and ethylenediaminetetraacetate ions has been examined. 相似文献
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R. N. Johnston W. Lockhart R. T. Ritchie D. H. Smith 《BMJ (Clinical research ed.)》1960,1(5173):592-595
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