A GENETICALLY MARKED-I ELEMENT IN DROSOPHILA-MELANOGASTER CAN BE MOBILIZED WHEN ORF2 IS PROVIDED IN TRANS

I factors in Drosophila melanogaster are non-LTR retrotransposons simi lar to mammalian LINEs. They transpose at very high frequencies in the germ line of SF females resulting from crosses between reactive femal es, devoid of active I factors, and inducer males, containing active I factors. The vermilion marked IviP2 element was designed to allow eas y phenotypical screening for-retrotransposition events. It is deleted in ORF2 and therefore cannot produce reverse transcriptase. IviP2 can be mobilized at very low frequencies by actively transposing I factors in the germ line of SF females. This paper shows that IviP2 can be mo bilized more efficiently in the germ line of strongly reactive females in the absence of active I factors, when it is trans-complemented by the product of ORF2 synthesized from the hsp70 heat-shock promoter. Th is represents a promising step toward tile use of marked I elements to study retrotransposition and as tools for mutagenesis.