The mutator effect of amber alleles of three early genes (43, 32, 47), which were suppressed by the bacterial suppressor gene, was studied. There are some advantages in using the suppressed amber alleles instead of ts, because in this case definite amino acid substitutions take place in the protein due to certain suppressor gene effect. For example, in Escherichia coli CR63(Su+-1) the replacement of the original amino acid by serine takes place. Studying the mutator effect of 43 alleles of DNA polymerase gene of phage T4 with tester mutant r131 showed that in condition of suppression by the gene Su+ -1 only 13,9% of alleles possessed the mutator activity. In the same experiments with mutants of genes 32 and 47 the mutator effect was not observed.