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1.
Fig. 2

Fig. 2. From: Novel mutator mutants of E. coli nrdAB ribonucleotide reductase: insight into allosteric regulation and control of mutation rates.

RNR mutator mutants discovered in this study and their location in the nrdA and nrdB genes. See text for the functional subdivision of mutants in groups 1, 2, and 3.

Deepti Ahluwalia, et al. DNA Repair (Amst). ;11(5):480-487.
2.
Fig. 3

Fig. 3. From: Novel mutator mutants of E. coli nrdAB ribonucleotide reductase: insight into allosteric regulation and control of mutation rates.

A model of the E. coli NrdAB holoenzyme with locations of discovered mutator mutations. The model is based on the reported crystal structures of the R1 [36] and R2 dimers [37], docked together into the holoenzyme as described in Materials and Methods.

Deepti Ahluwalia, et al. DNA Repair (Amst). ;11(5):480-487.
3.
Fig. 4

Fig. 4. From: Novel mutator mutants of E. coli nrdAB ribonucleotide reductase: insight into allosteric regulation and control of mutation rates.

Mutator effects of nrdAB mutator strains: two classes with differential response for lac G·C→T·A and A·T→T·A transversions and their correlation with group 1, 2, and 3 mutants. The red bar indicates the frequency of G·C→T·A transversions, the blue bar A·T→T·A transversions. The baseline values for the wild-type (wt) control were 1.6 × 10−8 (G·C→T·A) and 0.9 × 10−8 (A·T→T·A).

Deepti Ahluwalia, et al. DNA Repair (Amst). ;11(5):480-487.
4.
Fig. 1

Fig. 1. From: Novel mutator mutants of E. coli nrdAB ribonucleotide reductase: insight into allosteric regulation and control of mutation rates.

Outline of the genetic system used to obtain mutator mutants of E. coli carrying defects in the nrdAB genes. Plasmid pHABcat is mutagenized (*) in vitro with hydroxylamine and used to transform a strain containing plasmid pHABamp and a chromosomal nrdAB deletion. Replacement of pHABamp by pHABcat then allows scoring for a mutator phenotype based on colony papillation (lacZ reversion). See text and Materials and Methods for details.

Deepti Ahluwalia, et al. DNA Repair (Amst). ;11(5):480-487.
5.
Fig. 6

Fig. 6. From: Novel mutator mutants of E. coli nrdAB ribonucleotide reductase: insight into allosteric regulation and control of mutation rates.

dNTP pool changes predict mutational specificity. The diagrams show the lacZ sequence at which the G·C→T·A (top) or A·T→T·A (bottom) mutations occur. The red T indicates the misinserted ‘incorrect’ dTTP opposite the relevant template base (underlined), while the blue G or A indicates the ‘correct’ dGTP or dATP competing with the dTTP at the insertion step. The arrows represent the subsequent incorporation of dCTP (next nucleotide) and dATP (next-next nucleotide), which may protect the misinserted base against their exonucleolytic removal. See text for a full description.

Deepti Ahluwalia, et al. DNA Repair (Amst). ;11(5):480-487.
6.
Fig. 5

Fig. 5. From: Novel mutator mutants of E. coli nrdAB ribonucleotide reductase: insight into allosteric regulation and control of mutation rates.

Detail views of RNR features and mutated amino acid residues. (A) Close-up of the RNR activity site (ATP cone) with residues indicated that were found to yield a mutator phenotype. (B) Possible effect of the T55I mutation on (d)ATP binding. The isoleucine side chain intrudes in the nucleotide binding area and may interfere with effector binding. (C) Close-up of the R1-R2 interaction area with R1 and R2 mutator residues indicated. The proximity of R1 and R2 mutants coupled with their similar mutational properties and dNTP pool changes support a functional interaction and common mechanism. (D) A close-up view of the RNR specificity site showing important Loop 2 (red) and the G295 and A301 residues, which yield a mutator phenotype upon mutation.

Deepti Ahluwalia, et al. DNA Repair (Amst). ;11(5):480-487.

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