Protein determinants of insertional specificity for the Drosophila Gypsy retrovirus

The gypsy retrovirus invades the germ line of Drosophila females, inserting with a high frequency into the ovo locus. Gypsy insertion sites in ovo are clustered within a region in the promoter of the ovo gene that contains mu ltiple binding sites for the OvoA and OvoB proteins. We found that a 1.3-kb DNA fragment containing this region is able to confer gypsy insertional sp ecificity independent of its genomic location. The frequency of gypsy inser tions into the ovo gene is significantly lower in wild-type females than in ovo(D1) females. In addition, gypsy insertions in ovo(D1) females occur du ring most stages of germ-line development whereas insertions in wild-type f emales occur only in late stages. This pattern of temporally specific inser tions, as well as the higher frequency of insertion in ovo(D1) females, cor relates with the presence of the OvoA or OvoD1 proteins. The results sugges t that gypsy insertional specificity might be determined by the binding of the OvoA repressor isoform to the promoter region of the gene.