How did O'Donnell show that the sliding clamp complex actually slides along dsDNA providing processivity to DNA Pol III?

I think he took dna, a primer, and one radioactive dNTPs, added Pol III that was isolated, ran a gel, and the conclusion was that it was processive because on the gel, the distributive section had many bands and processive had one band. I dunno. does anyone know what the experiment was called and what the hypothesis was? Please, I want serious answers