Assuntos
Proteínas de Bactérias/química , Clostridium/enzimologia , Glucosiltransferases/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Clostridium/química , Clostridium/genética , Glucosiltransferases/genética , Glucosiltransferases/metabolismo , Modelos Moleculares , Especificidade por SubstratoRESUMO
The synthesis of the enzymes constituting the electron transport chain of Escherichia coli is controlled by electron acceptors in order to achieve high ATP yields and high metabolic rates as well. High ATP yields (or efficiency) are obtained by the use of electron acceptors for respiration which allow high ATP yields, preferentially O2, and nitrate in the absence of O2. The rate of metabolism is adjusted by use of respiratory isoenzymes which differ in the rate and the efficiency of energy conservation, such as the non-coupling NADH dehydrogenase II (ndh gene) and the coupling NADH dehydrogenase I (nuo genes). By combination of the contrary principles (rate versus efficiency), growth is optimized for growth yields and rates. One of the major transcriptional regulators controlling the switch from aerobic to anaerobic respiration is FNR (fumarate nitrate reductase regulator). FNR is located in the cytoplasm and contains a [4Fe-4S] cluster in the active (anaerobic) state. By reaction with O2 the cluster is converted to a [2Fe-2S] cluster and finally to apoFNR. O2 diffuses into the cytoplasm even at very low O2-tensions (1 microM) where it inactivates [4Fe-4S] x FNR. The formation of [4Fe-4S] x FNR from apoFNR can use glutathione as a reducing agent in vitro. This process could also be important for the reductive activation of FNR in vivo. A model for the control of the functional state of FNR by O2 and glutathione is discussed. According to this model the functional state of FNR is determined by a (rapid) inactivation of FNR by O2, and a slow (constant) reactivation with glutathione as the reducing agent.
Assuntos
Proteínas de Escherichia coli/efeitos dos fármacos , Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Regulação Bacteriana da Expressão Gênica , Proteínas Ferro-Enxofre/efeitos dos fármacos , Proteínas Ferro-Enxofre/metabolismo , Oxigênio/farmacologia , Escherichia coli/genética , Escherichia coli/fisiologia , Proteínas de Escherichia coli/genética , Proteínas Ferro-Enxofre/genética , Oxirredução , Transdução de SinaisRESUMO
CHD proteins are members of the chromo domain family, a class of proteins involved in transcription, DNA degradation and chromatin structure. In higher eukaryotes, there are two distinct subfamilies of CHD proteins: CHD1 and CHD3/4. Analyses carried out in vitro indicate that the CHD3/4 proteins may regulate transcription via alteration of chromatin structure. However, little is known about the role of CHD proteins in vivo, particularly the CHD1 subfamily. To understand better the cellular function of CHD proteins, we initiated a study on the Chd1p protein from budding yeast. Using genomic DNA arrays, we identified genes whose expression is affected by the absence of Chd1p. A synthetic-lethal screen uncovered genetic interactions between SWI/SNF genes and CHD1. Biochemical experiments using Chd1p purified from yeast showed that it reconfigures the structure of nucleosome core particles in a manner distinct from the SWI-SNF complex. Taken together, these results suggest that Chd1p functions as a nucleosome remodeling factor, and that Chd1p may share overlapping roles with the SWI-SNF complex to regulate transcription.
