Using genomic data to determine the diversity and distribution of target site motifs recognized by class C-attC group II introns.

The attC sites are well-known integrase-targeted elements involved in the insertion and excision of gene cassettes from integrons. Recently, functional analysis of Sma.I2, a class C-attC group II intron, showed that this mobile element invades the attC sites through a specific process. The analysis of genomic data indicates that class C-attC group II introns are independently acquired by their bacterial hosts and evolve in the recognition of a variety of target sites, including the attCs. In addition, adaptation of class C-attC group II introns seemed to be favourable for particular genera, such as Shewanella, suggesting a possible niche for the spread of class C-attC group II introns inserted at attC sites. This understanding suggests a functional role of short palindromic DNA sequences, such as the attCs, as important tools for the acquisition of mobile elements associated with horizontal gene transfer.