Insertion mutation inactivates the expression of the recessive oncogene lethal(2)giant larvae of Drosophila melanogaster

The Drosophila recessive oncogene lethal(2)giant larvae is located at the extreme left end of the second chromosome close to telomeric repetitive sequences. Of the 20 l(2)gl mutant alleles isolated from wild flies in widespread populations of the Soviet Union and California, all but two appear to represent large deletions which have removed the telomeric repetitive sequences and l(2)gl single copy sequences (Mechler et al. 1985). We have analyzed the structure of the two exceptions: the l(2)glGB52 mutation results from the insertion of a single transposable element of the B104 or roo family, whereas the more complex rearrangements of the l(2)glDV275 mutation consists of an 8 kb interstitial deletion whose breakpoints have become associated with a large transposed DNA fragment. Characterization of this fragment shows that it consists of B104 sequences flanked on one side by sequences originating from the chromosomal region 24D. Furthermore, we show that in both mutants normal transcription of the l(2)gl gene is abolished.