PROTEIN-PROTEIN INTERACTIONS BETWEEN THE ESCHERICHIA-COLI SINGLE-STRANDED DNA-BINDING PROTEIN AND EXONUCLEASE-I

It was demonstrated previously that a deoxyribophosphodiesterase (dRpa se) activity is associated with the DNA repair enzyme exonuclease I, a nd that this activity is stimulated by the addition of the E. coli sin gle-stranded DNA-binding protein (Ssb). This activity catalyzes the re lease of deoxyribose-phosphate groups at apurinic/apyrimidinic (AP) si tes in the DNA that have been cleaved by the action of an AP endonucle ase. We have now used the yeast two-hybrid system to demonstrate that a protein-protein interaction occurs between exonuclease I and Ssb. Wh en the E. coli ssb gene was fused in frame to the DNA-activating domai n of the GAL4 transcriptional activator and the exonuclease I gene was fused in frame to the DNA-binding domain, a functional GAL4 transcrip tional activator was produced as determined by growth of yeast on sele ctive medium and the measurement of beta-galactosidase activity. We ha ve also demonstrated that Ssb can stimulate the dRpase activity of exo nuclease I using double-stranded bacteriophage M13 DNA containing seve ral strand interruptions at incised AP sites. These results suggest th at Ssb may be required for efficient base-excision repair in bacteria. (C) 1996 by Radiation Research Society