Target site selection by the mariner-like element, Mos1.

The eukaryotic transposon Mos1 is a class-II transposable element that moves using a "cut-and-paste" mechanism in which the transposase is the only protein factor required. The formation of the excision complex is well documented, but the integration step has so far received less investigation. Like all mariner-like elements, Mos1 was thought to integrate into a TA dinucleotide without displaying any other target selection preferences. We set out to synthesize what is currently known about Mos1 insertion sites, and to define the characteristics of Mos1 insertion sequences in vitro and in vivo. Statistical analysis can be used to identify the TA dinucleotides that are non-randomly targeted for transposon integration. In vitro, no specific feature determining target choice other than the requirement for a TA dinucleotide has been identified. In vivo, data were obtained from two previously reported integration hotspots: the bacterial cat gene and the Caenorhabditis elegans rDNA locus. Analysis of these insertion sites revealed a preference for TA dinucleotides that are included in TATA or TA x TA motifs, or located within AT-rich regions. Analysis of the physical properties of sequences obtained in vitro and in vivo do not help to explain Mos1 integration preferences, suggesting that other characteristics must be involved in Mos1 target choice.