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While most missense suppressors have very narrow specificities and only suppress the allele against which they were isolated, the sumA missense suppressor from Salmonella enterica serovar Typhimurium is a promiscuous or broad-acting missense suppressor that suppresses numerous missense mutants. The sumA missense suppressor was identified as a glyV tRNA Gly3(GAU/C) missense suppressor that can recognize GAU or GAC aspartic acid codons and insert a glycine amino acid instead of aspartic acid. In addition to rescuing missense mutants caused by glycine to aspartic acid changes as expected, sumA could also rescue a number of other missense mutants as well by changing a neighboring (contacting) aspartic acid to glycine, which compensated for the other amino acid change. Thus the ability of sumA to rescue numerous missense mutants was due in part to the large number of glycine codons in genes that can be mutated to an aspartic acid codon and in part to the general tolerability and/or preference for glycine amino acids in proteins. Because the glyV tRNA Gly3(GAU/C) missense suppressor has also been extensively characterized in Escherichia coli as the mutA mutator, we demonstrated that all gain-of-function mutants isolated in a glyV tRNA Gly3(GAU/C) missense suppressor are transferable to a wild-type background and thus the increased mutation rates, which occur in glyV tRNA Gly3(GAU/C) missense suppressors, are not due to the suppression of these mutants.

The study demonstrated that biotinylation can facilitate the uptake of peptides up to 31 amino acids in length by Escherichia coli and that transport is dependent on the biotin transporter, BirB or BioP. It is concluded that uptake of biotinylated peptides could be competitively inhibited by free biotin or avidin and blocked by the protonophore CCCP, which disrupts membrane potential.

The alternative sigma factor, sigma-32, is accumulated when cytoplasmic precursors of secretory proteins collect together and stimulate the signal transmission for induction of heat shock protein synthesis. The aggregation of sigma-32 regulates the transcription of heat shock proteins, catalyzed by RNA polymerase. Mutations in secB or secA and excessive production of export-defective proteins are responsible for the aggregation of secretory protein precursors.

Abstract Background The efficient microbial utilization of lignocellulosic hydrolysates has remained challenging because this material is composed of multiple sugars and also contains growth inhibitors such as acetic acid (acetate). Using an engineered consortium of strains derived from Escherichia coli C and a synthetic medium containing acetate, glucose, xylose and arabinose, we report on both the microbial removal of acetate and the subsequent simultaneous utilization of the sugars. Results In a first stage, a strain unable to utilize glucose, xylose and arabinose (ALS1392, strain E. coli C ptsG manZ glk crr xylA araA) removed 3 g/L acetate within 30 hours. In a subsequent second stage, three E. coli strains (ALS1370, ALS1371, ALS1391), which are each engineered to utilize only one sugar, together simultaneously utilized glucose, xylose and arabinose. The effect of non-metabolizable sugars on the metabolism of the target sugar was minimal. Additionally the deletions necessary to prevent the consumption of one sugar only minimally affected the consumption of a desired sugar. For example, the crr deletion necessary to prevent glucose consumption reduced xylose and arabinose utilization by less than 15% compared to the wild-type. Similarly, the araA deletion used to exclude arabinose consumption did not affect xylose- and glucose-consumption. Conclusions Despite the modest reduction in the overall rate of sugar consumption due to the various deletions that were required to generate the consortium of strains, the approach constitutes a significant improvement in any single-organism approach to utilize sugars found in lignocellulosic hydrolysate in the presence of acetate.

Abstract We report a new approach for the simultaneous conversion of xylose and glucose sugar mixtures into products by fermentation. The process simultaneously uses two substrate-selective strains of Escherichia coli, one which is unable to consume glucose and one which is unable to consume xylose. The xylose-selective (glucose deficient) strain E. coli ZSC113 has mutations in the glk, ptsG and manZ genes while the glucose-selective (xylose deficient) strain E. coli ALS1008 has a mutation in the xylA gene. By combining these two strains in a single process, xylose and glucose are consumed more quickly than by a single-organism approach. Moreover, we demonstrate that the process is able to adapt to changing concentrations of these two sugars, and therefore holds promise for the conversion of variable sugar feed streams, such as lignocellulosic hydrolysates.

Pyruvate formation in Escherichia coli strain ALS929 containing mutations in the aceEF, pfl, poxB, pps, and ldhA genes that encode the pyruvate dehydrogenase complex, pyruvate formate lyase, pyruvate oxidase, phosphoenolpyruvate synthase, and lactate dehydrogenase, respectively is reported. Out of the four nutrient limitation conditions, growth under acetate limitation resulted in the highest glycolytic flux, pyruvate formation rate, and pyruvate yield.

A total of five matrine derivatives were synthesized and evaluated for their anti-proliferation activity using a panel of four human cancer cell lines, including A549 lung, BT20 breast, MCF-7 breast and U2OS osteosarcoma cells. The YF3-5, YF3-7 and YF3-9, three novel compounds, demonstrated increased anti-proliferation activity compared with matrine, of which YF3-5 revealed the strongest anti-proliferation activity with a half-maximal inhibitory concentration value of 15.49-16.67 µM against the four human cancer cell lines. The anti-proliferation mechanism underlying YF3-5 was investigated in the A549 human lung cancer cell line and the results demonstrated that YF3-5 exerted its anti-proliferation activity through the induction of apoptosis and oxidative stress, in addition to arresting the cell cycle at the G1 phase in a dose-dependent manner. [ABSTRACT FROM AUTHOR]