Pol III* dissociates from the beta clamp upon completing a template. [3H]Pol III* (labeled in the theta subunit) and [32P]betaPK (a derivative of beta containing six extra C-terminal amino acids; this derivative can be labeled with 32P from [gamma-32P]ATP using cAMP-dependent protein kinase) were assembled under idling conditions (only two dNTPs present) (panel A), or with all four dNTPs to fill in the gap (panel B). Reactions were gel filtered in column buffer containing 100 mM NaCl, and the fractions counted in a scintilation counter.