A small-molecule compound selectively inhibits Pol III. (A) The RU7 compound is titrated into β-dependent replication reactions by using Pol II (blue triangles), Pol III (red circles), or Pol IV (green diamonds). (B) The effect of RU7 on replication assays by using either the E. coli replication system (i.e., Pol III core, γ complex. and β clamp; red triangles) or the eukaryotic system (i.e., yeast Pol δ, RFC, and PCNA; green circles).