title: Exonuclease IX of Escherichia coli.
abstract: The bacteria Escherichia coli contains several exonucleases acting on both double- and single-stranded DNA and in both a 5'-->3' and 3'-->5' direction. These enzymes are involved in replicative, repair and recombination functions. We have identified a new exonuclease found in E.coli, termed exonuclease IX, that acts preferentially on single-stranded DNA as a 3'-->5' exonuclease and also functions as a 3'-phosphodiesterase on DNA containing 3'-incised apurinic/apyrimidinic (AP) sites to remove the product trans -4-hydroxy-2-pentenal 5-phosphate. The enzyme showed essentially no activity as a deoxyribophosphodiesterase acting on 5'-incised AP sites. The activity was isolated as a glutathione S-transferase fusion protein from a sequence of the E.coli genome that was 60% identical to a 260 bp region of the small fragment of the DNA polymerase I gene. The protein has a molecular weight of 28 kDa and is free of AP endonuclease and phosphatase activities. Exonuclease IX is expressed in E.coli , as demonstrated by reverse transcription-PCR, and it may function in the DNA base excision repair and other pathways.
authors.affiliation: Department of Radiology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Shafritz
authors.forename: M
authors.initials: M
authors.lastname: Sandigursky
authors.forename: W A
authors.initials: WA
authors.lastname: Franklin
mesh_terms: D004277:DNA, Single-Stranded / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D015870:Gene Expression; D010727:Phosphoric Diester Hydrolases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D004277:DNA, Single-Stranded; D005090:Exodeoxyribonucleases; C113094:exonuclease IX, E coli; D043211:Exodeoxyribonuclease V; D010727:Phosphoric Diester Hydrolases