Molecular genetics of a transposon-induced dominant mutation in the Drosophila locus Glued

The organization of the Drosophila locus Glued containing the dominant allele Gl was shown to differ from that of the normal locus by an insertion of a 9-kilobase-pair DNA segment near the 3' end of a transcribed region. The insertion causes the formation of a truncated polyadenylylated transcript of 5.1 kilobases instead of the normal 6.0 kilobases. The inserted DNA segment has the properties of a transposon and was identified by its corresponding restriction map as B104, which is a retrovirus-like transposon with direct terminal repeats. B104 appears to be oriented in Gl with the same polarity of transcription as Gl. The truncated Gl transcript terminates prematurely inside the 5' terminal repeat of B104, in the region of a putative polyadenylylation signal. We discuss the general implications of this finding for transposon- and retrovirus-induced mutagenesis and for the origin of dominant mutations.