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-alpha, (P)kay-beta and (P)kay-gamma. These three promoters lead to four different transcripts: kay-alpha, kay(sro), kay-beta and kay-gamma. (P)kay-alpha produces two different transcripts: kay-alpha and kay(sro) where the other two promoters, (P)kay-beta and (P)kay-gamma, produce a single transcript each. The transcripts kay-alpha, beta and gamma 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-alpha and beta. 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-alpha. 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.