Analyses of cis -acting elements that affect the transposition of Mos1 mariner transposons in vivo.

The left (5') inverted terminal repeat (ITR) of the Mos1 mariner transposable element was altered by site-directed mutagenesis so that it exactly matched the nucleotide sequence of the right (3') ITR. The effects on the transposition frequency resulting from the use of two 3' ITRs, as well as those caused by the deletion of internal portions of the Mos1 element, were evaluated using plasmid-based transposition assays in Escherichia coli and Aedes aegypti. Donor constructs that utilized two 3' ITRs transposed with greater frequency in E. coli than did donor constructs with the wild-type ITR configuration. The lack of all but 10 bp of the internal sequence of Mos1 did not significantly affect the transposition frequency of a wild-type ITR donor. However, the lack of these internal sequences in a donor construct that utilized two 3' ITRs resulted in a further increase in transposition frequency. Conversely, the use of a donor construct with two 3' ITRs did not result in a significant increase in transposition in Ae. aegypti. Furthermore, deletion of a large portion of the internal Mos1 sequence resulted in the loss of transposition activity in the mosquito. The results of this study indicate the possible presence of a negative regulator of transposition located within the internal sequence, and suggest that the putative negative regulatory element may act to inhibit binding of the transposase to the left ITR. The results also indicate that host factors which are absent in E. coli, influence Mos1 transposition in Ae. aegypti.