Abstract
The in vivo incorporation of 2-aminopurine into DNA of T4 bacteriophage allelic for gene 43 (DNA polymerase), mutator (L56), 43+ and antimutator (L141) was measured. The magnitude of incorporation (mol/mol of Thy) was 1/1500 in L56, 1/1600 in 43+ and 1/8900 in L141. The incorporation ratio L56:43+:L141 in vivo was equal to that mediated by the purified DNA polymerases of these allelic phages in vitro. A model for 2-aminopurine-induced A.cntdot.T .dblarw. G.cntdot.C transitions is discussed. The model is used to predict the magnitudes of replication errors (C mispairing with a template 2-aminopurine) and incorporation errors (2-aminopurine mispairing with a template C) per round of replication and to investigate the asymmetry in 2-aminopurine-induced transitions favoring the A.cntdot.T .fwdarw. G.cntdot.C pathway over G.cntdot.C .fwdarw. A.cntdot.T. The fidelity of L56 and L141 DNA polymerases probably exemplifies 1-step and 2-step editing, respectively.