Transposable element mariner
The mariner/Tc1 superfamily of transposable elements is one of the most diverse and widespread Class II transposable elements. Within the larger assemblage, the mariner-like elements (MLEs) and the Tc1-like elements (TLEs) are distinct families differing characteristically in the composition of the "D,D(35)E" cation-binding domain. Based on levels of sequence similarity, the elements in each family can be subdivided further into several smaller subfamilies. MLEs and TLEs both have an extraordinarily wide host range. They are abundant in insect genomes and other invertebrates and are found even in some vertebrate species including, in the case of mariner, humans.
A number of mariner transformation vectors based on the mauritiana subfamily of transposable elements were introduced into the genome of Drosophila melanogaster and examined for their ability to be mobilized by the mariner transposase. Simple insertion vectors were constructed from single mariner elements into which exogenous DNA ranging in size from 1.3-4.5 kb had been inserted; composite vectors were constructed with partial or complete duplications of mariner flanking the exogenous DNA. All of the simple insertion vectors showed levels of somatic and germline excision that were at least 100-fold lower than the baseline level of uninterrupted mariner elements. A composite vector consisting of two virtually complete elements flanking exogenous DNA yielded a frequency of somatic eye-color mosaicism far smaller than that observed for uninterrupted elements. These results are consistent with deletion analysis which indicates that, within the 1286 bp element, at least nucleotides 229-586, 735-765 and 939-1066 contain sequences that are necessary for transposase binding or that are needed to maintain proper spacing between binding sites. Hence efficient mobilization of mariner in vivo requires the presence and proper spacing of sequences internal to the element as well as the inverted repeats.