title: Exonuclease X of Escherichia coli. A novel 3'-5' DNase and Dnaq superfamily member involved in DNA repair.
abstract: DNA exonucleases are critical for DNA replication, repair, and recombination. In the bacterium Escherichia coli there are 14 DNA exonucleases including exonucleases I-IX (including the two DNA polymerase I exonucleases), RecJ exonuclease, SbcCD exonuclease, RNase T, and the exonuclease domains of DNA polymerase II and III. Here we report the discovery and characterization of a new E. coli exonuclease, exonuclease X. Exonuclease X is a member of a superfamily of proteins that have homology to the 3'-5' exonuclease proofreading subunit (DnaQ) of E. coli DNA polymerase III. We have engineered and purified a (His)(6)-exonuclease X fusion protein and characterized its activity. Exonuclease X is a potent distributive exonuclease, capable of degrading both single-stranded and duplex DNA with 3'-5' polarity. Its high affinity for single-strand DNA and its rapid catalytic rate are similar to the processive exonucleases RecJ and exonuclease I. Deletion of the exoX gene exacerbated the UV sensitivity of a strain lacking RecJ, exonuclease I, and exonuclease VII. When overexpressed, exonuclease X is capable of substituting for exonuclease I in UV repair. As we have proposed for the other single-strand DNA exonucleases, exonuclease X may facilitate recombinational repair by pre-synaptic and/or post-synaptic DNA degradation.
authors.affiliation: Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254-9110, USA.
authors.forename: M
authors.initials: M
authors.lastname: Viswanathan
authors.forename: S T
authors.initials: ST
authors.lastname: Lovett
mesh_terms: D001483:Base Sequence; D004249:DNA Damage; D017931:DNA Primers; D004260:DNA Repair; D004277:DNA, Single-Stranded / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D013379:Substrate Specificity; D014466:Ultraviolet Rays
chemical_list: D017931:DNA Primers; D004277:DNA, Single-Stranded