Nucleotide 5-MeCITP is an inhibitor of telomerase activity.

(A) Chemical structures and electron density surface potentials of indolyl nucleotide analogs used in this study. For clarity, only nucleobase structures are shown. Abbreviations at the bottom of each nucleobase correspond to the full name of the nucleotide as described in S1 Table. (B) Screening of nucleotide analogs via the direct telomerase activity assay reveals that 5-MeCITP reduces telomerase activity by 80% compared with untreated control. Numbers at the bottom of the gel correspond to the analog number indicated in panel A. Control refers to untreated reaction. Values to the left of the gel depict the number of deoxynucleotides added by telomerase to the primer d(GGGTTA)3. (C) Quantitation of G (dGTP) incorporation relative to control for samples analyzed in panel B. Error bars indicate the standard deviation calculated from three replicates. A two-tailed Student t test was used to determine p-values. *p p S1 Data). dATP, deoxyadenosine triphosphate; dGTP, deoxyguanosine triphosphate; LC, loading control; 5-MeITP, 5-methylindolyl-2′-deoxyriboside 5′-triphosphate; 4-NITP, 4-nitroindolyl-2′-deoxynucleoside 5′-triphosphate; 6-NITP, 6-nitroindolyl-2′-deoxynucleoside 5′-triphosphate; 5-AITP, 5-aminoindolyl-2′-deoxyriboside 5′-triphosphate; 5-CITP, 5-carboxylindolyl-2′-deoxyriboside 5′-triphosphate; 5-EyITP, 5-ethyleneindolyl-2′-deoxyriboside 5′-triphosphate; 5-MeCITP, 5-methylcarboxyl-indolyl-2′-deoxyriboside 5′-triphosphate.