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排序方式: 共有241条查询结果,搜索用时 93 毫秒
1.
Apurinic/apyrimidinic-specific endonuclease activities from Dictyostelium discoideum 总被引:1,自引:0,他引:1
Two apurinic/apyrimidinic- (AP-) specific endonuclease activities have been isolated from the cells of Dictyostelium discoideum by fractionation on DEAE-cellulose, CM-cellulose and Sephadex G-75. These activities, designated A and B, have apparent molecular weights of 49000 and 40000, respectively. Although their precise reaction optima differ somewhat, both A and B quantitatively nick AP DNA best at pH 8.0-8.5 in low salt (less than 100 mM NaCl); both require Mg2+. These activities are apparently specific only for AP sites in DNA. The low activities observed on heavily ultraviolet-irradiated DNA, gamma-irradiated DNA and osmium tetroxide-treated DNA are consistent with the small numbers of secondary AP sites expected in these DNAs. Both A and B produce single-strand nicks in AP DNA that result in termini that serve as good primers for Escherichia coli polymerase I. Hence, A and B appear to be Class II AP endonucleases which yield 3'-OH termini at nicks on the 5' side of baseless sugars. It is unclear whether A and B are independently coded proteins, different post-translational modifications of the same gene product, or whether one is an artifact arising from the isolation. Many of the properties of these D. discoideum AP endonuclease activities are similar to those of the predominant AP endonucleases observed in bacterial, plant and animal cells. They will be of use in the characterization of excision repair in this organism. 相似文献
2.
Binding specificity of the periplasmic oligopeptide-binding protein from Escherichia coli. 总被引:6,自引:2,他引:4
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The structural properties required for the binding of peptide substrates to the Escherichia coli periplasmic protein involved in oligopeptide transport were surveyed by measuring the ability of different peptides to compete for binding in an equilibrium dialysis assay with the tripeptide Ala-Phe-[3H]Gly. The protein specifically bound oligopeptides and failed to bind amino acids or dipeptides. Acetylation of the peptide amino terminus of (Ala)3 severely impaired binding, whereas esterification of the carboxyl terminus significantly reduced but did not completely eliminate binding. Peptides composed of L-amino acids competed more effectively than did peptides containing D-residues or glycine. Experiments with a series of alanyl peptide homologs demonstrated a decrease in competitive ability with increasing chain length beyond tripeptide. Competition studies with tripeptide homologs indicated that a wide variety of amino acyl side chains were tolerated by the periplasmic protein, but side-chain composition did affect binding. Fluorescence emission data suggested that this periplasmic protein possesses more than one substrate-binding site capable of distinguishing peptides on the basis of amino acyl side chains. 相似文献
3.
Purification and characterization of a periplasmic oligopeptide binding protein from Escherichia coli 总被引:5,自引:0,他引:5
C A Guyer D G Morgan N Osheroff J V Staros 《The Journal of biological chemistry》1985,260(19):10812-10818
We have purified and characterized an oligopeptide binding protein released from the periplasm of Escherichia coli W by mild osmotic shock. The purified protein was greater than 97% homogeneous as determined by either sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Mr = 60,000) or isoelectric focusing (pI = 5.95). The binding protein has a Stokes radius of 30 A and a sedimentation coefficient (s(0)20,w) of 4.6 S. Based on these hydrodynamic studies, the native protein has a molecular weight of 56,000. The tripeptide, Ala-Phe-[3H]Gly, which is transported via the shock-sensitive sensitive oligopeptide permease, binds to the purified protein in dilute solution with a Kd of 0.1 microM and a stoichiometry of approximately 1 to 1. Results from this study support the hypothesis that this periplasmic oligopeptide binding protein functions in the initial recognition of peptide substrates for the oligopeptide permease system. 相似文献
4.
Use of chromosomal integration in the establishment and expression of blaZ, a Staphylococcus aureus beta-lactamase gene, in Bacillus subtilis 总被引:19,自引:12,他引:7
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C W Saunders B J Schmidt M S Mirot L D Thompson M S Guyer 《Journal of bacteriology》1984,157(3):718-726
With several different vectors, attempts were made to establish blaZ, a Staphylococcus aureus beta-lactamase gene, in Bacillus subtilis. Stable establishment of blaZ in B. subtilis was achieved by use of a vector that allowed the integration of a single copy of the gene into the chromosome of that host. blaZ was expressed in the heterologous host since B. subtilis strains carrying integrated blaZ produced beta-lactamase and were more resistant to ampicillin than was wild-type B. subtilis. blaZ was stably inherited in such strains, as no loss of the ability to produce beta-lactamase was observed after growth in nonselective liquid medium or on solid medium. In contrast, a blaZ-containing restriction fragment could not be established in B. subtilis with either pUB110- or pC194-based vectors. Similarly, a pC194-based shuttle vector (pGX318) containing the 5' end of blaZ (including the promoter and the coding region for the signal sequence and the first few amino acids of the mature protein) was unable to transform B. subtilis. Two derivatives of pGX318 that could be stably established in B. subtilis were isolated. The structures of these derivatives suggested that inactivation of the blaZ promoter was associated with the acquisition of the ability to be established. 相似文献
5.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
6.
Evidence for a Reductive Pathway for the Anaerobic Metabolism of Benzoate 总被引:18,自引:6,他引:12
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Evidence is presented for a reductive pathway for the anaerobic metabolism of benzoate by Rhodopseudomonas palustris. 相似文献
7.
8.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献
9.
Molecular phylogeny and divergence times of drosophilid species 总被引:32,自引:15,他引:17
The phylogenetic relationships and divergence times of 39 drosophilid
species were studied by using the coding region of the Adh gene. Four
genera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (from
Hawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, and
Sophophora--were included. After conducting statistical analyses of the
nucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNA
genes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophila
as the outgroup. The phylogenetic tree obtained showed that the first major
division of drosophilid species occurs between subgenus Sophophora (genus
Drosophila) and the group including subgenera Drosophila and Engiscaptomyza
plus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is then
divided into D. willistoni and the clade of D. obscura and D. melanogaster
species groups. In the other major drosophilid group, Zaprionus first
separates from the other species, and then D. immigrans leaves the
remaining group of species. This remaining group then splits into the D.
repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila,
Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightly
clustered. Each of the D. repleta, D. obscura, and D. melanogaster groups
is monophyletic. The splitting of subgenera Drosophila and Sophophora
apparently occurred about 40 Mya, whereas the D. repleta group and the
Hawaiian drosophilid cluster separated about 32 Mya. By contrast, the
splitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya,
suggesting that Scaptomyza experienced a rapid morphological evolution. The
D. obscura and D. melanogaster groups apparently diverged about 25 Mya.
Many of the D. repleta group species studied here have two functional Adh
genes (Adh-1 and Adh-2), and these duplicated genes can be explained by two
duplication events.
相似文献
10.
From electrophoresis experiments it is concluded that acidic phospholipids incorporated in liquid crystalline phosphatidylcholine bilayers at neutral pH are randomly distributed. The same is true for spin-labelled fatty acids. In contrast, long chain fatty acids are not fully ionized at neutral pH and appear to be clustered, i.e. they segregate out into patches. Only at is the fatty acid-COOH group fully ionized and charge repulsion leads to a random distribution of the fatty acid within the plane of the bilayer. 相似文献