The sequence specificity of bleomycin damage in three cloned DNA sequences that differ by a small number of base substitutions.

The DNA sequence specificity of the cancer chemotherapeutic agent, bleomycin, has been investigated in three clones of human alpha RI-DNA. The three 340-base pair alpha RI-DNA sequences were almost identical in their nucleotide sequence enabling the study of subtle effects of base substitutions on bleomycin cleavage. By utilizing densitometer scanning and statistical analysis of the degree of bleomycin DNA cleavage, we found 17 significant differences between the three DNA sequences. Eleven of these differences could be attributed to base substitutions close to the dinucleotide cleavage site. However, six of the differences were at positions two or more base pairs from the base substitution sites. The significant differences were up to 12 base pairs from base substitutions. It is proposed that these long range effects are due to base substitutions causing microvariation in the DNA structure to which bleomycin cleavage is sensitive.