CRYSTAL-STRUCTURES OF THE KLENOW FRAGMENT OF THERMUS-AQUATICUS DNA-POLYMERASE-I COMPLEXED WITH DEOXYRIBONUCLEOSIDE TRIPHOSPHATES

The crystal structures of the Klenow fragment of the Thermus aquaticus DNA polymerase I (Klentaql) complexed with four deoxyribonucleoside t riphosphates (dNTP) have been determined to 2.5 Angstrom resolution. T he dNTPs bind adjacent to the O helix of Klentaql. The triphosphate mo ieties are at nearly identical positions in all four complexes and are anchored by three positively charged residues, Arg659, Lys663, and Ar g587, and by two polar residues, His639 and Gln613. The configuration of the base moieties in the Klentaql/dNTP complexes demonstrates varia bility suggesting that dNTP binding is primarily determined by recogni tion and binding of the phosphate moiety. However, when superimposed o n the Tag polymerase/blunt end DNA complex structure (Eom et al., 1996 ), two of the dNTP/Klentaql structures demonstrate appropriate stackin g of the nucleotide base with the 3' end of the DNA primer strand, sug gesting that at least in these two binary complexes, the observed dNTP conformations are functionally relevant.