Limits...
G-quadruplex preferentially forms at the very 3' end of vertebrate telomeric DNA.

Tang J, Kan ZY, Yao Y, Wang Q, Hao YH, Tan Z - Nucleic Acids Res. (2007)

Bottom Line: This property provides a molecular basis for telomerase inhibition by G-quadruplex formation.Moreover, it may also regulate those processes that depend on the structure of the very 3' telomere end, for instance, the alternative lengthening of telomere mechanism, telomere T-loop formation, telomere end protection and the replication of bulky telomere DNA.Therefore, targeting telomere G-quadruplex may influence more telomere functions than simply inhibiting telomerase.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biochemistry and Biophysics, College of Life Sciences, Wuhan University, Wuhan 430072, PR China.

ABSTRACT
Human chromosome ends are protected with kilobases repeats of TTAGGG. Telomere DNA shortens at replication. This shortening in most tumor cells is compensated by telomerase that adds telomere repeats to the 3' end of the G-rich telomere strand. Four TTAGGG repeats can fold into G-quadruplex that is a poor substrate for telomerase. This property has been suggested to regulate telomerase activity in vivo and telomerase inhibition via G-quadruplex stabilization is considered a therapeutic strategy against cancer. Theoretically G-quadruplex can form anywhere along the long G-rich strand. Where G-quadruplex forms determines whether the 3' telomere end is accessible to telomerase and may have implications in other functions telomere plays. We investigated G-quadruplex formation at different positions by DMS footprinting and exonuclease hydrolysis. We show that G-quadruplex preferentially forms at the very 3' end than at internal positions. This property provides a molecular basis for telomerase inhibition by G-quadruplex formation. Moreover, it may also regulate those processes that depend on the structure of the very 3' telomere end, for instance, the alternative lengthening of telomere mechanism, telomere T-loop formation, telomere end protection and the replication of bulky telomere DNA. Therefore, targeting telomere G-quadruplex may influence more telomere functions than simply inhibiting telomerase.

Show MeSH

Related in: MedlinePlus

Distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 detected by the 3′ exonuclease activity of T4 polymerase. (A) Gel electrophoresis of hydrolysis products of T24(TTAGGG)7 and the four reference oligonucleotides designated to form G-quadruplex at desired positions leaving a tail of 3, 2, 1, 0 repeats of T6 at the 3′ end, respectively. (B) Densitometry scans of the gel shown in A). (C) Quantified distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 with incomplete hydrolysis calibrated. Data are the mean of three independent experiments with standard deviation.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2275102&req=5

Figure 5: Distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 detected by the 3′ exonuclease activity of T4 polymerase. (A) Gel electrophoresis of hydrolysis products of T24(TTAGGG)7 and the four reference oligonucleotides designated to form G-quadruplex at desired positions leaving a tail of 3, 2, 1, 0 repeats of T6 at the 3′ end, respectively. (B) Densitometry scans of the gel shown in A). (C) Quantified distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 with incomplete hydrolysis calibrated. Data are the mean of three independent experiments with standard deviation.

Mentions: Incomplete hydrolysis was observed (see the first three reference lanes in Figure 5A). Calibration was made for this in each of the structural isoforms in T24(TTAGGG)7, which was calculated as (intensity ratio of the undigested/digested band in the relevant reference lane) × (intensity of the digest product of a corresponding structural isoform of T24(TTAGGG)7).


G-quadruplex preferentially forms at the very 3' end of vertebrate telomeric DNA.

Tang J, Kan ZY, Yao Y, Wang Q, Hao YH, Tan Z - Nucleic Acids Res. (2007)

Distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 detected by the 3′ exonuclease activity of T4 polymerase. (A) Gel electrophoresis of hydrolysis products of T24(TTAGGG)7 and the four reference oligonucleotides designated to form G-quadruplex at desired positions leaving a tail of 3, 2, 1, 0 repeats of T6 at the 3′ end, respectively. (B) Densitometry scans of the gel shown in A). (C) Quantified distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 with incomplete hydrolysis calibrated. Data are the mean of three independent experiments with standard deviation.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2275102&req=5

Figure 5: Distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 detected by the 3′ exonuclease activity of T4 polymerase. (A) Gel electrophoresis of hydrolysis products of T24(TTAGGG)7 and the four reference oligonucleotides designated to form G-quadruplex at desired positions leaving a tail of 3, 2, 1, 0 repeats of T6 at the 3′ end, respectively. (B) Densitometry scans of the gel shown in A). (C) Quantified distribution of G-quadruplex formation at different positions in T24(TTAGGG)7 with incomplete hydrolysis calibrated. Data are the mean of three independent experiments with standard deviation.
Mentions: Incomplete hydrolysis was observed (see the first three reference lanes in Figure 5A). Calibration was made for this in each of the structural isoforms in T24(TTAGGG)7, which was calculated as (intensity ratio of the undigested/digested band in the relevant reference lane) × (intensity of the digest product of a corresponding structural isoform of T24(TTAGGG)7).

Bottom Line: This property provides a molecular basis for telomerase inhibition by G-quadruplex formation.Moreover, it may also regulate those processes that depend on the structure of the very 3' telomere end, for instance, the alternative lengthening of telomere mechanism, telomere T-loop formation, telomere end protection and the replication of bulky telomere DNA.Therefore, targeting telomere G-quadruplex may influence more telomere functions than simply inhibiting telomerase.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biochemistry and Biophysics, College of Life Sciences, Wuhan University, Wuhan 430072, PR China.

ABSTRACT
Human chromosome ends are protected with kilobases repeats of TTAGGG. Telomere DNA shortens at replication. This shortening in most tumor cells is compensated by telomerase that adds telomere repeats to the 3' end of the G-rich telomere strand. Four TTAGGG repeats can fold into G-quadruplex that is a poor substrate for telomerase. This property has been suggested to regulate telomerase activity in vivo and telomerase inhibition via G-quadruplex stabilization is considered a therapeutic strategy against cancer. Theoretically G-quadruplex can form anywhere along the long G-rich strand. Where G-quadruplex forms determines whether the 3' telomere end is accessible to telomerase and may have implications in other functions telomere plays. We investigated G-quadruplex formation at different positions by DMS footprinting and exonuclease hydrolysis. We show that G-quadruplex preferentially forms at the very 3' end than at internal positions. This property provides a molecular basis for telomerase inhibition by G-quadruplex formation. Moreover, it may also regulate those processes that depend on the structure of the very 3' telomere end, for instance, the alternative lengthening of telomere mechanism, telomere T-loop formation, telomere end protection and the replication of bulky telomere DNA. Therefore, targeting telomere G-quadruplex may influence more telomere functions than simply inhibiting telomerase.

Show MeSH
Related in: MedlinePlus