Repression of the Ac-transposase gene promoter by Ac transposase

Mobility of the maize Ac-Ds transposable element family depends on the production of Ac-encoded transposase (TPASE). The TPASE is a DMA-binding protein which recognizes internal sites near both Ac termini in a region which overlaps the putative TPASE gene promoter. Therefore, it was hypothesized that TPASE may regulate its own transcription. The TPASE effect on Ac promoter activity was tested in transgenic tobacco plants and in protoplasts transformed with Ac-promoter-β-glucuronidase gene fusions. It was found that TPASE can repress Ac promoter activity in cotyledons and leaves of transgenic plants, as well as in transient assays in protoplasts. TPASE-mediated repression occurs independently of the presence of the Ac untranslated leader or of the 3′ termini. When fused to a deleted (-67) cauliflower mosaic virus 35S promoter, the first 237 bp of Ac (starting from the 5′ end) are sufficient to enable TPASE-mediated repression. The results indicate that TPASE can act as a transcriptional repressor. The possible mechanisms and significance of TPASE-mediated repression are discussed.