Inhibition of DNA chain growth by alpha-2'-deoxythioguanosine

Mecca lymphosarcoma cells were incubated with (35-S)-alpha-2'-deoxythioguanosine for 8 hr and DNA was analyzed in alkaline sucrose gradients. 35-S radioactivity was found exclusively in a low-molecular-weight fraction. Pulse-chase experiments showed that 35-S-containing DNA fragments formed during the pulse were not incorporated into high-molecular-weight DNA following the chase. These results, together with the previous observation that (35-S)-alpha-2'-deoxythioguanosine was found predominantly in the terminal nucleoside position of DNA chains, suggested that alpha-2'deoxythioguanosine, once incorporated, terminates chain elongation.