Fatty acid uptake in <i>Escherichia coli</i>: regulation by recruitment of fatty acyl-CoA synthetase to the plasma membrane

Fatty acid uptake in Escherichia coli has been shown to be inhibited by starvation and to be reversed by a short preincubation of the starved cells with D- or L-lactate, succinate, and acetate; these effects on oleate uptake were due to regulation of the rate-limiting step which involves fatty acyl-CoA synthetase. Investigation into the mechanism of regulation of fatty acyl-CoA synthetase showed that D-lactate did not affect the activity of the enzyme directly. Fatty acyl-CoA synthetase was found to be activated by about 20-fold by Triton X-100 and by another 4-fold by the addition of bacterial membranes. D-Lactate treatment was shown to result in coisolation of fatty acyl-CoA synthetase with the plasma membrane; these results are consistent with the interpretation that recruitment of the enzyme to the plasma membrane by D-lactate results in its activation and consequently in the increased level of fatty acid uptake.Key words: fatty acid, uptake, regulation, recruitment, fatty acyl-CoA synthetase, Escherichia coli, plasma membrane. </jats:p

<i>Schizosaccharomyces pombe</i>, unlike<i>Saccharomyces cerevisiae</i>, may not directly regulate nuclear-cytoplasmic transport of spliced tRNAs in response to nutrient availability

Eukaryotic cells adapt to changes in nutrient levels by regulating key processes, such as gene transcription, ribosome biogenesis, and protein translation. Several studies have shown that nuclear export of tRNAs is also regulated in Saccharomyces cerevisiae and rat hepatoma H4IIE cells during nutrient stress. However, recent studies suggest that nutrient stress does not affect nuclear tRNA export in several mammalian cell lines, including rat hepatoma H4IIE. Furthermore, in contrast to previous studies, data reported more recently established that nuclear export of mature tRNAs derived from intron-containing pre-tRNAs, but not mature tRNAs made from intronless precursors, is affected by nutrient stress in several species of Saccharomyces , but not in the yeast Kluyveromyces lactis . Here, we provide evidence suggesting that Schizosaccharomyces pombe , like mammalian cells and K. lactis, but unlike Saccharomyces, do not directly regulate nuclear export of mature tRNAs made from intron-containing pre-tRNAs in response to nutrient stress. These studies collectively suggest that regulation of nuclear export of spliced tRNAs to the cytoplasm in response to nutrient availability may be limited to the genus Saccharomyces, which unlike other yeasts and higher eukaryotes produce energy for fermentative growth using respiration-independent pathways by downregulating the citric acid cycle and the electron transport chain.</jats:p

Synthesis of acyl-CoA thioesters

An improved synthesis of fatty acyl coenzyme A has been developed that permits the synthesis of highly radioactive fatty acyl coenzyme A derivatives and thus can be used for the synthesis of high specific activity photoaffinity labels. Conditions were developed to solubilize the coenzyme A in anhydrous solvent for the acylation. The complete activation of fatty acid to the imidazolide is described and the acylation of the coenzyme A under anhydrous conditions was shown to result in the conversion of the fatty acid to the fatty acyl coenzyme A derivative. The synthetic product was shown by its chemical and biochemical reactivity to be the pure thioester of coenzyme A. The purification of the fatty acyl coenzyme A by reverse-phase chromatography is described. The yield of pure fatty acyl coenzyme A was essentially quantitative.Key words: acyl coenzyme A, N,N′-carbonyldiimidazole, high pressure liquid chromatography, imidazolide, synthesis. </jats:p

Plants, like mammals, but unlike<i>Saccharomyces,</i>do not regulate nuclear-cytoplasmic tRNA trafficking in response to nutrient stress

Cells respond to nutrient stress by regulating gene transcription and various key metabolic processes, including ribosome biogenesis and protein synthesis. Several studies have shown that yeasts and mammalian cells also regulate export of tRNAs from the nucleus to the cytosol in response to nutrient stress. However, nuclear export of tRNA in mammalian cells during nutrient stress is controversial, as it has been recently shown that nuclear-cytoplasmic transport of tRNAs in several mammalian cell lines is not affected by nutrient deprivation. Furthermore, contrary to previous studies, data reported recently indicate that nuclear export of mature tRNAs derived from intron-containing precursor tRNAs, but not tRNAs made from intronless precursors, is affected by nutrient availability in several Saccharomyces species, although not in Kluyveromyces lactis and Schizosaccharomyces pombe. Here, we report that plants, like mammals and some yeasts, but unlike Saccharomyces, do not directly regulate nuclear export of tRNA in response to nutrient stress, indicating that this process is not entirely conserved among evolutionarily diverse organisms