IS2-43 and IS2-44: new alleles of the insertion sequence IS2 which have promoter activity.

The sequence of two new IS2 alleles with promoter activity (IS2-43 and IS2-44) is reported. The alleles are identical and are formed by a 17 bp tandem duplication in an AT-rich region of IS2. This created a new RNA polymerase binding site. A mutation was found that increased the frequency of formation of these 17 bp duplications but not of another class of duplications, the "mini-insertions". This suggested that the mechanisms of formation of the two classes of duplications are different.