Specific primer extension with 3′-O-(2-cyanoethyl)-dNTP derivatives by RevertAid M-MuLV reverse transctiptase. A) Set of DNA substrates used for specificity studies (* indicates radiolabelled 5′-termini). The position in the template strand that directs the nucleotide to be incorporated is in bold type. B) The initial primer-extension step (lanes 2, 4, 6, 8, and 10) was followed by the addition of a dNTP mixture to the solution containing all four natural dNTPs dissolved in water and incubation for 5 min (lanes 3, 5, 7, 9, and 11). Lanes 1 and 12: the starting-material primer set; 2 and 3: 3′-O-(2-cyanoethyl)-dGTP; 4 and 5: 3′-O-(2-cyanoethyl)-dATP; 6 and 7: 3′-O-(2-cyanoethyl)-dTTP; 8 and 9: 3′-O-(2-cyanoethyl)-dCTP; 10 and 11: full set of 3′-O-(2-cyanoethyl)-dNTP nucleotides.