an enzymatically active dna polymerase or active fragment thereof , having at least 80 % identity in its amino acid sequence to the dna polymerase of thermoanaerobacter thermohydrosulfuricus or fragment thereof , and having an amino acid alteration at position 720 in tts pol i or at position 426 in δtts pol i or at a homologous position defined with respect to tts dna ploymerase i , having improved incorporation of nucleotide analogs and natural bases during dna synthesis compared to unaltered enzyme .