COMPARISON OF TARGETED-GENE REPLACEMENT FREQUENCIES IN DROSOPHILA-MELANOGASTER AT THE FORKED AND WHITE LOCI

P element-induced gene conversion has been previously used to modify t he white gene of Drosophila melanogaster in a directed fashion. The ap plicability of this approach of gene targeting in Drosophila melanogas ter, however, has not been analyzed quantitatively for other genes. We took advantage of the P element-induced forked allele, f(hd), which w as used as a target, and we constructed a vector containing a modified forked fragment for converting f(hd). Conversion frequencies were ana lyzed for this locus as well as for an alternative white allele, w(eh8 12). Combination of both P element-induced mutant genes allowed the si multaneous analysis of conversion frequencies under identical genetic, developmental, and environmental conditions. This paper demonstrates that gene conversion through P element-induced gap repair can be appli ed with similar success rates at the forked locus and in the white gen e. The average conversion frequency at forked was 0.29%, and that at w hite was 0.17%. These frequencies indicate that in vivo gene targeting in Drosophila melanogaster should be applicable for other genes in th is species at manageable rates. We also confirmed the homolog dependen ce of reversions at the forked locus, indicating that P elements trans pose via a cut-and-paste mechanism. In a different experiment, we atte mpted conversion with a modified forked allele containing the su(Hw) b inding site. Despite an increased sample size, there were no conversio n events with this template. One interpretation (under investigation) is that the binding of the su(Hw) product prevents double-strand break repair.