Drosophila Rrp1 3'-exonuclease: demonstration of DNA sequence dependence and DNA strand specificity.

Drosophila Rrp1 (recombination repair protein 1) is a DNA repair enzyme whose nuclease activities include AP-endonuclease, 3'-exonuclease, 3'-phosphodiesterase and 3'-phosphatase. This study investigates the sequence specificity of the dsDNA 3'-exonuclease activity of Rrp1. We demonstrate that the activity is more efficient in purine-rich regions of dsDNA than in pyrimidine-rich regions. Rrp1 exonuclease activity is examined at 3'-terminal homopurine or homopyrimidine tracts, at junctions between purine- and pyrimidine-rich sequences and upon encountering repeated dinucleotide runs. The data show that purine-purine and 3'-pyrimidine-5'-purine dinucleotide bonds are cleaved faster than 3'-purine-5'-pyrimidine or pyrimidine-pyrimidine bonds. Thus, the base occupying the penultimate position in the 3'-terminal dinucleotide may be important in determining the relative efficiency of bond cleavage by Rrp1. These findings may reflect upon specific DNA-protein interactions in the enzyme active site.