Figure 1.

Structure and structural rationale for mutating Drosophila PCNA. A: amino acid sequences of the interdomain loops of Drosophila (designated D.m.) and human (designated H.s.) PCNA. Gray boxes indicate amino acids identical for both organisms; arrows show amino acids thought essential for interaction of human PCNA with human pol δ. Amino acid 123 is the only one which is both essential and different in Drosophila versus human PCNA. B: the "front" side of the human PCNA trimer. Amino acids 119-133 of the interdomain loops are highlighted by showing their α-carbon atoms as black spheres. The α-carbon atom of Val123 is shown as a larger gray sphere.