RESUMO
Acetyl-CoA Carboxylase catalyzes the first committed step in fatty acid synthesis. Escherichia coli acetyl-CoA carboxylase is composed of biotin carboxylase, carboxyltransferase and biotin carboxyl carrier protein functions. The accA and accD genes that code for the alpha- and beta-subunits, respectively, are not in an operon, yet yield an alpha(2)beta(2) carboxyltransferase. Here, we report that carboxyltransferase regulates its own translation by binding the mRNA encoding its subunits. This interaction is mediated by a zinc finger on the beta-subunit; mutation of the four cysteines to alanine diminished nucleic acid binding and catalytic activity. Carboxyltransferase binds the coding regions of both subunit mRNAs and inhibits translation, an inhibition that is relieved by the substrate acetyl-CoA. mRNA binding reciprocally inhibits catalytic activity. Preferential binding of carboxyltransferase to RNA in situ was shown using fluorescence resonance energy transfer. We propose an unusual regulatory mechanism by which carboxyltransferase acts as a 'dimmer switch' to regulate protein production and catalytic activity, while sensing the metabolic state of the cell through acetyl-CoA concentration.
Assuntos
Acetil-CoA Carboxilase/genética , Carboxil e Carbamoil Transferases/genética , Proteínas de Escherichia coli/genética , Regulação Bacteriana da Expressão Gênica , Regulação Enzimológica da Expressão Gênica , Biossíntese de Proteínas , Acetil-CoA Carboxilase/química , Acetil-CoA Carboxilase/metabolismo , Sítios de Ligação , Carboxil e Carbamoil Transferases/química , Carboxil e Carbamoil Transferases/metabolismo , Catálise , DNA/metabolismo , Escherichia coli/enzimologia , Escherichia coli/genética , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Subunidades Proteicas/biossíntese , Subunidades Proteicas/genética , Subunidades Proteicas/metabolismo , RNA Mensageiro/química , RNA Mensageiro/metabolismo , Dedos de ZincoRESUMO
RNA virus populations display extreme sequence variation. It is thought that this heterogeneity is advantageous to the population, permitting adaptation to rapidly changing environments that present varying types and degrees of selective pressure. A consequence of this efficient evolution of RNA viruses is the susceptibility of these viruses to compounds that further increase sequence variation as these agents force the virus into error catastrophe. Therefore, lethal mutagenesis, induction of error catastrophe, represents an important, untapped strategy for development of antiviral agents. This article briefly describes the theoretical and experimental data supporting lethal mutagenesis as an antiviral strategy and discusses host and viral mechanisms for development of resistance to ribavirin, a representative of this class of antiviral agents.