The Saccharomyces cerevisiae Dna2 protein plays an important role in maintenance of the trinucleotide repeated sequences

초록

The Dna2 protein is responsible for the primary removal of RNA primers in eukaryotic Okazaki fragments. It consists of an N-terminal non-catalytic domain and two separate catalytic domains, one for ssDNA-specific endonuclease and the other for helicase activities. Deletion of its N-terminal 405 amino acid domain did not cause any loss of the two enzymatic activities of Dna2. However, yeast cells with a mutant DNA2 allele (dna2Δ405N) lacking the N-terminal domain were severely impaired in growth at 37℃, indicating that this region is critical for a cellular function(s) of Dna2. In order to understand the biological role of the N-terminal domain, we examined and compared the enzymological properties of Dna2Δ405N mutant enzyme with those of wild type one. Wild type Dna2 efficiently cleaved and unwound the substrates with trinucleotide repeated (TNR) sequences, whereas, the mutant enzyme poorly utilized the substrates. Consistent with this, the purified N-terminal 405 amino acid protein bound to the substrate, but the mutant protein lacking this domain did not. We also observed instability of TNR in the dna2Δ405N mutant strain. This suggests Dna2 has a role in maintaining TNR in the eukaryotes, and the N-terminal domain is important for this function of Dna2.