2.2–2.3 Å with Rfree values of 23–25% (Table 1).
The overall structure of each loop mutant 3Dpol does
not change significantly as compared to the wild-type
polymerase, and a maximum likelihood multiple
structure alignment performed by the program THESEUS
[11,12] indicates that all changes resulting from
each mutation are isolated to movements within and
around residues 288–292 (Fig. 1C). The binding of
GTP does not significantly change the structure of the
mutants as both the apo structures and NTP
complexes have essentially identical backbone traces
with the GTP binding into the same site as in the
wild-type enzyme (PDB entry 1RA7 [10,13]). The
exception to this is the weakly ordered and chemically
modified S288A loop that moves to the in conformation
due to a steric clash with the bound GTP.
Composite simulated-annealing omit maps of all the
structures are shown in Fig. 2.