Abstract
The Dna2 protein is a multifunctional enzyme with 5'-3' DNA helicase, DNA-dependent ATPase, 3' exo/endonuclease, and 5' exo/endonuclease. The enzyme is highly specific for structures containing single-stranded flaps adjacent to duplex regions. We report here two novel activities of both the yeast and human Dna2 helicase/nuclease protein: single strand annealing and ATP-independent strand exchange on short duplexes. These activities are independent of ATPase/helicase and nuclease activities in that mutations eliminating either nuclease or ATPase/helicase do not inhibit strand annealing or strand exchange. ATP inhibits strand exchange. A model rationalizing the multiple catalytic functions of Dna2 and leading to its coordination with other enzymes in processing single-stranded flaps during DNA replication and repair is presented.
Highlights
Yeast Dna2 protein3 is a helicase/nuclease involved in the maintenance of genome stability [1]
Rad27 pol3-01, and dna2-1 pol3-01 double mutants are both inviable [1, 15]. This may suggest that the absence of pol ␦ 3Ј to 5Ј exonuclease activity leads to excessive strand displacement and creation of long flap substrates that would require the cooperative action of FEN1 and Dna2 for processing [14]
We examined the effect of NaCl on strand annealing by Yeast Dna2 protein (yDna2)
Summary
Rad pol, and dna pol double mutants are both inviable [1, 15] This may suggest that the absence of pol ␦ 3Ј to 5Ј exonuclease activity leads to excessive strand displacement and creation of long flap substrates that would require the cooperative action of FEN1 and Dna for processing [14]. Based on the shared annealing/exchange properties of Dna, BLM, and WRN, we propose a model that suggests how the newly discovered activities may contribute to the efficient processing of flap structures in lagging strand replication intermediates. This model may reconcile the apparent paradox that two helicases of opposing polarities may perform redundant tasks leading to indistinguishable products
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