Efficiency of integron cassette insertion in correct orientation is ensured by the interplay of the three unpaired features of attC recombination sites

摘要: The integron is a bacterial recombination system that allows acquisition, stockpiling and expression of cassettes carrying protein-coding sequences, responsible for the emergence rise multiresistance in Gram-negative bacteria. functionality this depends on insertion promoterless correct orientation, allowing their from promoter located upstream cassette array. Correct orientation ensured by strand selectivity integrases bottom sites (attC), recombined form folded single-stranded hairpins. Here, we investigated basis such comparing wild-type mutated attC with different lengths, sequences structures. We show all three unpaired structural features distinguish top strands contribute to selectivity. localization Extra-Helical Bases (EHBs) directly favors integrase binding strand. Unpaired Central Spacer (UCS) Variable Terminal Structure (VTS) influence indirectly, probably through stabilization resulting synapse due nucleotide skew between two strands. These results underscore importance nature site tight control over orientation.