The gene structure of the Drosophila melanogaster proto-oncogene, kayak, and its nested gene, fos-intronic gene

We present herein a new model for the structure of the Drosophila kayak gene as well as preliminary data on the functional differences of its various isoforms. kayak is a homolog of the human proto-oncogene, c-fos. kayak has three different starts of transcription, and therefore promoters (P)kay-α, (P)kay-β and (P)kay-γ. These three promoters lead to four different transcripts: kay-α, kay^sro, kay-β and kay-γ. (P)kay-α produces two different transcripts: kay-α and kay^sro where the other two promoters, (P)kay-β and (P)kay-γ, produce a single transcript each. The transcripts kay-α, β and γ all splice into the mainbody of the kay gene, which codes for the DNA binding domain and leucine zipper; kay^sro is not spliced. Also, within this region is a nested gene, fos-intronic gene (fig) which is transcribed in the opposite direction. fig codes for a predicted PP2C phosphatase. fig has two different promoters which produce two different transcripts, both in the same reading frame, fig-α and β. This is an unusual gene structure for Drosophila. Only 13% of Drosophila genes have multiple promoters and only 7% have a nested gene. RT-PCR was performed on each transcript to determine the relative amounts of each RNA produced. All spliced kay transcripts appear to have equal abundance. The unspliced kay^sro transcript has a lower abundance than kay-α. Both fig transcripts are also detected in all stages tested. Lethal phase analysis and complementation testing suggest that the three isoforms of kayak may have different functions.