In order to gain insights into the structural basis of the multifunctional Dna2 enzyme involved in Okazaki fragment processing, we performed biochemical, biophysical and genetic studies to dissect the domain structure of Dna2.Proteolytic digestion of Dna2 using subtilisin produced a 127 k Da polypeptide that lacked the 45 k Da N-terminal region of Dna2.These included six histidines (bold) and the Xpress epitope (underlined) fused to its N-terminal methionine to facilitate detection and purification of the recombinant Dna2 proteins.HX-Dna2N behaved similarly to HX-Dna2 in chromatographic steps and was purified using the same procedure described for HX-Dna2 (7).
Recombinant Dna2 isolated from insect cells was shown to possess intrinsic ss DNA-specific endonuclease activity in addition to helicase activity (7).
The possible mode of regulation of Dna2 is discussed based upon our recent finding that replication protein A interacts functionally and physically with Dna2 during Okazaki fragment processing.
encodes a 172 k Da protein that is a multifunctional enzyme and thus has been implicated in several different aspects of DNA transactions (1–6).
A DNA substrate used to examine endonuclease activity of the Dna2 proteins was prepared by hybridizing a 73mer to ΦX174 ssc DNA as described (7).
The substrate contains a free 21 nt ss DNA 5′-tail connected to a 52 bp duplex.