shalter

5 • • •

TT'"’ -^OH 3'

I I I

3' • • •    ■ ■

Telomeric DNA

5' ^-AACCCCAAC ( Telomerase RNA j w-/

dGTP + dTTP

pp, polymerize

5 • • ♦ 3' • ••

TTGGGGTTG-o* I I I I I I I I I 5' ^-AACCCCAAC

^•3'    5'

translocate

5' .... 3' ....

5'

TTGGGGTTG-°^H 3'

¹¹^CCCAAC

-A A i

■ Figurę 25-24 Mechanism for the synthesis of telomeric DNA by Tetrahymena telomerase. The telomeres 5'-ending slrand is later extended by normal lagging slrand synthesis. [After Greider, C.W. and Blackbum. E.H., Naturę 337.336 (1989),]_

R

■ Figurę 25-25 Structure of the telomeric oligonucleotide d(GGGGTTTTGGGG). (a) The basc-pairing interactions in the G-quartet. (b) Schematic diagram of the NMR structure in which the slrand directions are indicated by arrows. The nudeotides are numbered 1 to 12 in one strand and 1* to 12* in the symmetry-related strand. Guaninc residues G1 to G4 are represented by blue rectangles,

G9 to G12 are cyan. Gl* to G4* are red, and G9* to G12* are pink. |After Schult/e. P. Smith. F.W.. and Fcigon. J.. Structure 2. 227 (1994). PUBid I56P.I_