http://www.jbc.org/content/249/14/4545.full.pdf

Exonuclease VII of Escherichia coli PURIFICATION AND PROPERTIES

Exonuclease VII of Escherichia coli. Mechanism of action.

Publisher Summary The chapter discusses the physiology of the mycobacteria. The chapter discusses physiology to cover not only the mycobacterial cell, its structure and organization, but also the properties that the organisms must have—first to enable them to survive once having gained entry to a host, and secondly to bring about the various changes that are subsequently manifested in the host. The structure of the mycobacterial cell has been the subject of a great deal of investigation. The prime emphasis has been on the nature of the cell wall, which not only is one of the thickest to be found in microorganisms but has a pronounced hydrophobicity because of an abundance of highly complex lipophilic macromolecules within it. The importance of lipids to the physiology of the mycobacterial cell is probably three-fold. Firstly, lipids, especially the mycolic acids, form an integral part of the structure of the cell wall; secondly, the high content of lipid associated with the cell wall gives the cell many of its outward characteristics (e.g. hydrophobicity, impenetrability to many materials); and thirdly by their more specific immunogenic and antigenic properties, many of the interactions between host-tissue and invading mycobacteria are seen to have their origins.

The Physiology of the Mycobacteria

Studies on a nuclease from Ustilago maydis. I. Purification, properties, and implication in recombination of the enzyme.

Publisher Summary Exonuclease V (exoV) enzymes are ubiquitous in bacteria. These enzymes belong to a larger group of ATP-dependent DNases and DNA-dependent ATPases, which also includes enzymes such as type-I restriction endonucleases, helicases, and gyrases. All these enzymes exhibit ATP-dependent double-stranded DNA exonuclease and DNA-dependent ATPase activities. In addition, ATP-dependent single-stranded DNA exonuclease, ATP-stimulated single-stranded DNA endonuclease, and ATP-dependent DNA unwinding may also be associated with the enzyme. Mechanism of action of the exoV enzyme indicates that DNA unwinding is fundamental to several of the enzyme's activities and can be its most important function in the cell. The complete degradation of DNA to acid-soluble oligonucleotides may only serve a function in restriction. The observation of decreased or undetectable exoV activity in recombination and repair mutants in certain bacteria has sparked a great deal of interest in these enzymes. Recombination and repair lesions in bacteria that lack exoV are not absolute, so the deficiency must be carefully quantitated with well-defined strains.

Martin F. Lavin

Papers

Partial purification and properties of a nucleoside triphosphate-dependent deoxyribonuclease from Mycobacterium smegmatis.