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131.
Studies of the binding of Escherichia coli RNA polymerase to DNA. V. T7 RNA chain initiation by enzyme-DNA complexes 总被引:9,自引:0,他引:9
Initiation of T7 RNA chains by Escherichia coli RNA polymerase-T7 DNA complexes has been followed using incorporation of λ-32P-labeled ATP and GTP to determine the relation between the enzyme binding sites and RNA chain initiation sites on the T7 genome. If the period of RNA synthesis is limited to less than two minutes, the stoichiometry of RNA chain initiation can be measured in the absence of chain termination and re-initiation. About 70% of the RNA polymerase holoenzyme molecules in current enzyme preparations are able to rapidly initiate a T7 RNA chain. The ratio of ATP- to GTP-initiated T7 RNA chains is not altered by variations in the number of enzyme molecules added per DNA, nor by alterations in the ionic conditions employed for RNA synthesis. This suggests that RNA chain initiation sites are chosen randomly through binding of RNA polymerase to tight (class A) binding sites on T7 DNA. 相似文献
132.
In vitro zygotic embryo culture of wild banana significantly increased the germination compared to greenhouse grown seeds. Embryo orientation and BAP concentration significantly affected germination rate. These factors together with gelling agent, dark and light conditions and coconut water, also showed variable effects on the number of roots per plant, root length, shoot length, number of days to root emergence and number of days to shoot emergence. 相似文献
133.
Modified norcantharidins; synthesis, protein phosphatases 1 and 2A inhibition, and anticancer activity 总被引:9,自引:0,他引:9
Hart ME Chamberlin AR Walkom C Sakoff JA McCluskey A 《Bioorganic & medicinal chemistry letters》2004,14(8):1969-1973
Fourteen modified norcantharidin analogues have been synthesised and screened for their ability to inhibit the serine/threonine protein phosphatases 1 and 2A. The most potent compounds found were 10 (PP1 IC(50)=13+/-5 microM; PP2A IC(50)=7+/-3 microM) and 16 (PP1 IC(50)=18+/-8 microM; PP2A IC(50)=3.2+/-0.4 microM). Overall, only analogues possessing at least one acidic residue at the former anhydride warhead displayed any PP1 or PP2A inhibitory action. The ability of these analogues to inhibit PP1 and PP2A correlates well with their observed anti-cancer activity against a panel of five cancer cell lines: A2780 (human ovarian carcinoma), G401 (human kidney carcinoma), HT29 (human colorectal carcinoma), H460 (human lung carcinoma) and L1210 (murine leukemia). 相似文献
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A quantitative assay for bacterial RNA polymerases. 总被引:23,自引:0,他引:23
M J Chamberlin W C Nierman J Wiggs N Neff 《The Journal of biological chemistry》1979,254(20):10061-10069
137.
A Richter J W Conlan M E Ward S G Chamberlin P Alexander N G Richards D E Davies 《Biochemistry》1992,31(40):9546-9554
Solubilized epidermal growth factor receptor (EGF-R) has been used in an extension of the Geysen epitope mapping protocol in order to provide additional insight into the amino acid residues in human transforming growth factor alpha (hTGF alpha) which are critical to recognition and binding. Overlapping heptapeptides which encompassed the 50 amino acid primary sequence of hTGF alpha were synthesized on a polyethylene solid phase, and the amount of detergent-solubilized EGF-R bound to each peptide was measured using ELISA. EGF-R appeared to bind reproducibly to four heptapeptides cognate to sequences in both the N- and C-domains of hTGF alpha (residues 22-28, 28-34, 36-42, and 44-50). Visualization of these four regions on three-dimensional solution phase structures of hTGF alpha, derived from 1H NMR measurements [Kline, T.-P., Brown, F.K., Brown, S.C., Jeffs, P.W., Kopple, K.D., & Mueller, L. (1990) Biochemistry 29, 7805-7813], indicated that the peptide segments are located on a single face of the protein and suggested the presence of a potential receptor binding cavity. If peptide segments within both the N- and C-domains of hTGF alpha are involved in binding to EGF-R, then this has direct consequences for possible molecular mechanisms by which receptor activation might take place. For example, the observed conformational flexibility in the six NMR-derived hTGF alpha structures due to variations in the main-chain torsion angles of Val-33, in combination with the involvement of residues from both domains in the proposed binding cavity, may imply that receptor activation results from interdomain reorientation in the protein ligand.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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