Figure 2.

Comparison of the effects of 7-deaza-GTP on the synthesis of ‘G–-adder’ slippage products. (A) RNA products in a 10 min reaction at 37°C, containing 0.2 µM promoter DNA, 0.2 µM T7 RNA polymerase and 400 µM GTP (left) or 7-deaza-GTP (right), in a buffer of 20 mM HEPES pH 7.8, 25 mM potassium glutamate, 0.025% Tween-20, 2.5 mM Tris, 15 mM Mg(OAc)₂, 0.25 mM EDTA. Both reactions contained trace amounts (<0.06 µM) of [α-³²P]GTP for detection. The part of the gel showing the ‘regular’ G-ladder has been overexposed to make the difference between the two more apparent. (B) Structures of a G-quartet and of guanine and its 7-deaza analog. Note that replacement of guanine in the quartet structure by 7-deaza-guanine destroys the stability of the quartet. (C) Plots of percent fall-off as a function of the transcript length.