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Some problems of mutagenesis induced by base analogues.

A brief survey is presented on the problem of base-analogue-induced mutagenesis. The main conclusions are as follows: (i) Since some of the base analogues may induce the SOS response, the probability exists that, in these cases, some of the mutants may arise via umuC-mediated misrepair mutagenesis; (ii) At least two cellular systems may influence base-analogue-induced mutagenesis: DNA polymerases and mismatch repair systems. Whereas the first may influence the yield of mutations, the second may affect both the yield and specificity of mutations; (iii) Specificity of base-analogue-induced mutations is much more differentiated than hitherto believed. Some of the base analogues are highly specific mutagens, e.g. N4- hydroxycytidine , which induces almost exclusively AT----GC base-pair transitions, whereas the others, e.g. 2-aminopurine and 2-amino-N6- methoxyadenine , may induce both transitions and transversions.