Modified polymerases for improved incorporation of nucleotide analogues
The invention relates to modified polymerase enzymes which exhibit improved incorporation of nucleotide analogs bearing substituents at the 3′ position of the sugar moiety that are larger in size than the naturally occurring 3′ hydroxyl group. Also described are methods of using the polymerases to incorporate nucleotides into polynucleotides, particularly in the context of DNA sequencing.
1. An altered 9° N DNA polymerase, comprising the sequence of SEQ ID NO: 14, wherein the first amino acid of the motif A region is mutated to alanine (A); the second amino acid of the motif A region is mutated to alanine (A); and the third amino acid of the motif A region is mutated to an amino acid selected from the group consisting of serine (S), alanine (A), glycine (G), and the amino acids having beta-branched side chains, whereby the altered 9° N DNA polymerase is capable of incorporating a 3′ O-azidomethyl-modified nucleotide.
2. The polymerase according to claim 1 which exhibits an increased rate of incorporation of the modified nucleotides, compared to 9° N DNA polymerase.
3. The polymerase according to claim 1 which is capable of incorporating modified nucleotides containing each of the four bases A, T, C and G.
4. The polymerase according to claim 1 which is capable of incorporating modified nucleotides at a reaction temperature of 30° C.
5. The polymerase according to claim 1 which is capable of incorporating modified nucleotides at reaction temperatures across the full range of 30° C. to 80° C.
6. The polymerase according to claim 1 , wherein the third amino acid of the motif A region is mutated to isoleucine (I), threonine (T), valine (V) or leucine (L).
7. An altered 9° N DNA polymerase, comprising the sequence of SEQ ID NO: 14, wherein the first amino acid of the motif A region is mutated to alanine (A); the second amino acid of the motif A region is mutated to alanine (A); and the third amino acid of the motif A region is mutated to an amino acid selected from the group consisting of serine (S), alanine (A), glycine (G), and the amino acids having beta-branched side chains, whereby the altered 9° N DNA polymerase is capable of incorporating a 3′ O-azidomethyl-modified nucleotide, further comprising at least one substitution mutation from amino acid 141 or 143 to an amino acid that is not negatively charged, whereby exonuclease activity is removed.
8. The polymerase according to claim 1 , wherein the third amino acid of the motif A region is mutated to serine (S), alanine (A) or glycine (G).
9. The polymerase according to claim 1 , further comprising at least one amino acid substitution mutation in the motif B region, whereby the activity of the polymerase is enhanced, with the proviso that said at least one amino acid substitution mutation does not include the exact combination of 409V and 485L.
10. The polymerase according to claim 9 , wherein the substitution mutation in the motif B region is to the second amino acid.
11. The polymerase according to claim 10 , wherein the substitution mutation is to an amino acid selected from the group consisting of F, I, S, V and C.
12. The polymerase according to claim 10 , wherein the substitution mutation is to L.
13. The polymerase according to claim 9 , wherein the motif B substitution mutations are to G at the first amino acid position and L at the third.
14. The polymerase according to claim 9 , wherein the motif B substitution mutations are to N at the first amino acid position and Q at the third.
15. The polymerase according to claim 9 , wherein the motif B substitution mutations are to those substitutions selected from the group consisting of SKN, GRD, KHN, ISN and THH.
16. The polymerase according to claim 1 , further comprising at least one substitution mutation in the motif C region.
17. The polymerase according to claim 16 , wherein the motif C region comprises at least one substitution mutation.
18. An altered 9° N DNA polymerase, comprising the sequence of SEQ ID NO: 14, wherein the first amino acid of the motif A region is mutated to alanine (A); the second amino acid of the motif A region is mutated to alanine (A); and the third amino acid of the motif A region is mutated to an amino acid selected from the group consisting of serine (S), alanine (A), glycine (G), and the amino acids having beta-branched side chains, whereby the altered 9° N DNA polymerase is capable of incorporating a 3′ O-azidomethyl-modified nucleotide, further comprising at least one amino acid substitution mutation in the motif B region, whereby the activity of the polymerase is enhanced, with the proviso that said at least one amino acid substitution does not include the exact combination of 409V and 485L, and which comprises at least one substitution mutation from amino acid 141 or 143 to an amino acid that is not negatively charged, whereby exonuclease activity is removed.