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Repair of O6-methylguanine adducts in human telomeric G-quadruplex DNA by O6-alkylguanine-DNA alkyltransferase.

Hellman LM, Spear TJ, Koontz CJ, Melikishvili M, Fried MG - Nucleic Acids Res. (2014)

Bottom Line: Its functions with short single-stranded and duplex substrates have been characterized, but its ability to act on other DNA structures remains poorly understood.Here, we examine the functions of this enzyme on O(6)-methylguanine (6mG) adducts in the four-stranded structure of the human telomeric G-quadruplex.This distinction may reflect differences in the conformational dynamics of 6mG residues in G-quadruplex DNAs.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biochemistry, Center for Structural Biology, University of Kentucky, Lexington, KY 40536, USA.

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Related in: MedlinePlus

Summary of kinetics results for the repair of telomere-sequence DNAs by AGT. (A) Amplitudes of kinetic phases. Fast phases (represented by A1 in Equation 4) are graphed as black bars. Amplitudes of slow phases (A2 in Equation 4) are graphed as medium gray bars. The sums of amplitudes (A1 + A2) are shown as light gray bars. No slow phases were detected for G1 and G5 DNAs in TEA buffer. (B) Reaction rates for the fast phase (upper panel) and the slow phase (lower panel). Fast-phase rates were similar for all DNAs except the 22-mer G11. Extending that sequence by 3 nt at the 3’-end (25-mer G11) gave a DNA that was repaired with a rate similar to those of 6mG residues at other positions. Fast-phase rates are similar for folded DNAs (KCl buffer) and unfolded DNAs (TEA buffer). Rates for slow phases are ∼1/10 to ∼1/60 of those of the corresponding fast phases. No slow phase was detectible for DNAs in TEA buffer.
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Figure 8: Summary of kinetics results for the repair of telomere-sequence DNAs by AGT. (A) Amplitudes of kinetic phases. Fast phases (represented by A1 in Equation 4) are graphed as black bars. Amplitudes of slow phases (A2 in Equation 4) are graphed as medium gray bars. The sums of amplitudes (A1 + A2) are shown as light gray bars. No slow phases were detected for G1 and G5 DNAs in TEA buffer. (B) Reaction rates for the fast phase (upper panel) and the slow phase (lower panel). Fast-phase rates were similar for all DNAs except the 22-mer G11. Extending that sequence by 3 nt at the 3’-end (25-mer G11) gave a DNA that was repaired with a rate similar to those of 6mG residues at other positions. Fast-phase rates are similar for folded DNAs (KCl buffer) and unfolded DNAs (TEA buffer). Rates for slow phases are ∼1/10 to ∼1/60 of those of the corresponding fast phases. No slow phase was detectible for DNAs in TEA buffer.

Mentions: For G-quadruplexes annealed and repaired in buffer containing KCl, a comparison of the amplitudes of the fast and slow reaction phases with the extent of repair is informative (Figure 8A). The amplitudes of the fast phase and reaction extent after long incubation (8.8 h) vary with position within the quadruplex, with greater values at positions G1, G3, G4 and G6 (located in outer tetrads, Figure 1), and smaller values for positions G2 and G5 (inner tetrads). Repair amplitudes for the inner tetrad residue G11, both in the standard 22-mer sequence and in an elongated 25-nt version, were similar to those at the other inner positions. This pattern suggests models in which the stacking of G-quartets influences the amplitude of the fast phase of the reaction as well as the overall extent of repair.


Repair of O6-methylguanine adducts in human telomeric G-quadruplex DNA by O6-alkylguanine-DNA alkyltransferase.

Hellman LM, Spear TJ, Koontz CJ, Melikishvili M, Fried MG - Nucleic Acids Res. (2014)

Summary of kinetics results for the repair of telomere-sequence DNAs by AGT. (A) Amplitudes of kinetic phases. Fast phases (represented by A1 in Equation 4) are graphed as black bars. Amplitudes of slow phases (A2 in Equation 4) are graphed as medium gray bars. The sums of amplitudes (A1 + A2) are shown as light gray bars. No slow phases were detected for G1 and G5 DNAs in TEA buffer. (B) Reaction rates for the fast phase (upper panel) and the slow phase (lower panel). Fast-phase rates were similar for all DNAs except the 22-mer G11. Extending that sequence by 3 nt at the 3’-end (25-mer G11) gave a DNA that was repaired with a rate similar to those of 6mG residues at other positions. Fast-phase rates are similar for folded DNAs (KCl buffer) and unfolded DNAs (TEA buffer). Rates for slow phases are ∼1/10 to ∼1/60 of those of the corresponding fast phases. No slow phase was detectible for DNAs in TEA buffer.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4150771&req=5

Figure 8: Summary of kinetics results for the repair of telomere-sequence DNAs by AGT. (A) Amplitudes of kinetic phases. Fast phases (represented by A1 in Equation 4) are graphed as black bars. Amplitudes of slow phases (A2 in Equation 4) are graphed as medium gray bars. The sums of amplitudes (A1 + A2) are shown as light gray bars. No slow phases were detected for G1 and G5 DNAs in TEA buffer. (B) Reaction rates for the fast phase (upper panel) and the slow phase (lower panel). Fast-phase rates were similar for all DNAs except the 22-mer G11. Extending that sequence by 3 nt at the 3’-end (25-mer G11) gave a DNA that was repaired with a rate similar to those of 6mG residues at other positions. Fast-phase rates are similar for folded DNAs (KCl buffer) and unfolded DNAs (TEA buffer). Rates for slow phases are ∼1/10 to ∼1/60 of those of the corresponding fast phases. No slow phase was detectible for DNAs in TEA buffer.
Mentions: For G-quadruplexes annealed and repaired in buffer containing KCl, a comparison of the amplitudes of the fast and slow reaction phases with the extent of repair is informative (Figure 8A). The amplitudes of the fast phase and reaction extent after long incubation (8.8 h) vary with position within the quadruplex, with greater values at positions G1, G3, G4 and G6 (located in outer tetrads, Figure 1), and smaller values for positions G2 and G5 (inner tetrads). Repair amplitudes for the inner tetrad residue G11, both in the standard 22-mer sequence and in an elongated 25-nt version, were similar to those at the other inner positions. This pattern suggests models in which the stacking of G-quartets influences the amplitude of the fast phase of the reaction as well as the overall extent of repair.

Bottom Line: Its functions with short single-stranded and duplex substrates have been characterized, but its ability to act on other DNA structures remains poorly understood.Here, we examine the functions of this enzyme on O(6)-methylguanine (6mG) adducts in the four-stranded structure of the human telomeric G-quadruplex.This distinction may reflect differences in the conformational dynamics of 6mG residues in G-quadruplex DNAs.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biochemistry, Center for Structural Biology, University of Kentucky, Lexington, KY 40536, USA.

Show MeSH
Related in: MedlinePlus