MOLECULAR CHARACTERIZATION OF HOBO-MEDIATED INVERSIONS IN DROSOPHILA-MELANOGASTER

The structure of chromosomal inversions mediated by hobo transposable elements in the Uc-1 X chromosome was investigated using cytogenetic a nd molecular methods. Uc-l contains a phenotypically silent hobo eleme nt inserted in an intron of the Notch locus. Cytological screening ide ntified six independent Notch mutations resulting from chromosomal inv ersions with one breakpoint at cytological position 3C7, the location of Notch. In situ hybridization to salivary gland polytene chromosomes determined that both ends of each inversion contained hobo and Notch sequences. Southern blot analyses showed that both breakpoints in each inversion had hobo-Notch junction fragments indistinguishable in stru cture from those present in the Uc-1 X chromosome prior to the rearran gements. Polymerase chain reaction amplification of the 12 hobo-Notch junction fragments in the six inversions, followed by DNA sequence ana lysis, determined that each was identical to one of the two hobo-Notch junctions present in Uc-l. These results are consistent with a model in which hobo-mediated inversions result from homologous pairing and r ecombination between a pair of hobo elements in reverse orientation.