By performing DNase I footprint and band-shift analyses of a 170-base-pair region of the murine thymidine kinase promoter, we identified an inducible DNA binding activity that we named Yi. Yi binding activity was not detected in G0 and G1 extracts, but it was observed as cells crossed the G1/S boundary. Yi proteins bind specifically to a consensus sequence (CCCNCNNNCT) found at three distinct sites in this promoter region. We also observed a murine Sp1 binding activity that was constitutive throughout the cell cycle. We propose that the G1/S-specific Yi binding is important for murine thymidine kinase gene regulation and perhaps also for initiation of DNA synthesis. 相似文献
Most Mycobacterium tuberculosis rifampin-resistant strains have been associated with mutations in an 81-bp rifampin resistance-determining region (RRDR) in the gene rpoB. However, if this region alone were targeted, rifampin-resistant strains with mutations outside the RRDR would not be detected. In this study, among 51 rifampin-resistant clinical isolates analyzed by sequencing 1,681-bp-long DNA fragments containing the RRDR, 47 isolates contained mutations within the RRDR, three isolates contained mutations both within and outside the RRDR, and only one isolate had a single missense mutation (Arg548His) located outside the RRDR. A drug susceptibility test of recombinant Mycobacterium smegmatis and M. tuberculosis isolates carrying mutated rpoB (Arg548His) showed an increased MIC for rifampin compared to that of the control strains. Modeling of the Arg548His mutant RpoB-DNA complex revealed that the His548 side chain formed a more stable hydrogen bond structure than did Arg548, reducing the flexibility of the rifampin-resistant cluster II region of RpoB, suggesting that the RpoB Arg548His mutant does not effectively interact with rifampin and results in bacterial resistance to the drug. This is the first report on the relationship between the mutation in codon 548 of RpoB and rifampin resistance in tuberculosis. The novel mutational profile of the rpoB gene described here will contribute to the comprehensive understanding of rifampin resistance patterns and to the development of a useful tool for simple and rapid drug susceptibility tests. 相似文献
The evolution of wavelike surface undulations in a thin polymer film under thermal stress in the presence of immobilized film spanning nanoparticles (NPs) is investigated. The elastic stresses in the plane of the polymer thin films is induced by fixed lateral constraints within the film (immobilized NPs) that resist in‐plane film thermal expansion as the temperature increases. Wavelike surface undulations arising from stress relaxation are observed as the thin‐film systems are heated above the glass‐transition temperature (Tg). The thermal stress affects both the characteristic wavelengths and the amplitudes of the wavelike surface undulations. Although the origin is different, the dynamic evolution of these wavelike undulations is strikingly similar in characteristics to spinodal decomposition. As compared with typical spinodal‐decomposition kinetics in liquid systems in which the early and intermediate stages are difficult to probe due to the narrow range of time scales, the overall evolutionary process of the wavelike surface undulations in NP‐filled polymer thin films is captured. The growth of the wavelike undulations shows characteristic time dependencies at the intermediate and late stages of instability.
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