JORDAN, AN ACTIVE VOLVOX TRANSPOSABLE ELEMENT SIMILAR TO HIGHER-PLANTTRANSPOSONS

We have isolated a 1595-bp transposable element from the multicellular green alga Volvox carteri following its insertion into the nitrate re ductase (nitA) locus. This element, which we have named Jordan, has sh ort (12-bp) terminal inverted repeats and creates a 3-bp target site d uplication, like some higher plant transposons of the classic type. Co ntained within the first 200 bp of one end of the element are 55-bp in verted repeats, one of which begins with the terminal inverted repeat. Revertants of the transposon insertion into the nitA locus were obtai ned at a rate of approximately 10(-4) per Volvox embryo per generation . In each revertant examined, all transposon sequences were completely excised, but footprints containing both sets of duplicated bases, in addition to three to nine extra bases, were left behind. Jordan contai ns no significant open reading frames and so appears to be nonautonomo us. DNA gel blot analysis indicates that Jordan is a member of a large family of homologous elements in the Volvox genome. We have isolated and characterized several of these homologs and found that they contai n termini very similar to those of Jordan. Efforts to utilize Jordan a nd its homologs as tools to tag and clone developmentally interesting genes of Volvox are discussed.