Folyt1, a new member of the hAT family, is active in the genome of the plant pathogen Fusarium oxysporum

An active transposable element, Folyt1, has been isolated from the tomato p athogen Fusarium oxysporum f. sp. lycopersici as an insertion sequence with in the coding region of the nitrate reductase gene (nit 1) in two independe nt mutants (CO66 and CO108). Folyt1 was 2615 bp in length and contained 9-b p imperfect inverted terminal repeats (ITRs) and 8 bp duplicated at the tar get site upon insertion, The element contained a long open reading frame in terrupted by a single putative intron. The predicted amino acid sequence sh owed similarity to conserved domains of transposases from hobo, Ac, and Tam 3 elements, which belong to the hAT family. The excision frequency of Folyt 1 was determined to be less than 10(-5) in both mutants. These events resto red the nit 1 wild-type allele without leaving footprints in all the revert ants of strain CO66. Nevertheless, some revertants of strain CO108 showed a point mutation footprint at the target sequence. Expression of the Folyt1 transposase was detected by Northern analysis as a 2.1-kb transcript. The e lement exists in about 10 copies per genome in F. oxysporum f. sp. lycopers ici and appears to be widely distributed among different formae speciales o f F. oxysporum. (C) 1999 Academic Press.