Transposition effect of adenine (Dam) methylation on activity of O end mutants of IS50.

The two ends of insertion sequence IS50 (from Tn5) differ in sequence and in activity during transposition: the IS50 I end contains DNA adenine methylation (Dam) sites and is affected directly by Dam methylation, whereas the O end lacks Dam sites. The effect of Dam methylation on the transposition of IS50-derived elements with base substitution mutations in their O ends was assayed to understand better how the divergent O and I ends interact. Of 31 O end mutations tested, ten impaired transposition less, and two impaired transposition more in Dam- than in Dam+ cells. These results suggest that the interaction between the two ends in a transposition complex is affected by the sequence or the extent of methylation of one end.