Control of Drosophila paramyosin/miniparamyosin gene expression - Differential regulatory mechanisms for muscle-specific transcription

To define the transcriptional mechanisms contributing to stage- and tissue- specific expression of muscle genes, we performed transgenic analysis of Dr osophila paramyosin gene regulation. This gene has two promoters, one for p aramyosin and one for miniparamyosin, which are active in partially overlap ping domains. Regions between -0.9 and -1.7 kilobases upstream of each init iation site contribute to the temporal and spatial expression patterns. By comparing the Drosophila melanogaster and Drosophila virilis promoters, con served binding sites were found for known myogenic factors, including one M EF2 site and three E boxes. In contrast with previous data, our experiments with the paramyosin promoter indicate that the MEF2 site is essential but not sufficient for proper paramyosin gene transcription. Mutations in the t hree E boxes, on the other hand, do not produce any effect in embryonic/lar val muscles. Thus MEF2 site- and E box-binding proteins can play different roles in the regulation of different muscle-specific genes, For the minipar amyosin promoters, several conserved sequences were shown to correspond to functionally important regions. Our data further show that the two promoter s work independently. Even when both promoters are active in the same muscl e fiber, the transcription driven by one of the promoters is not affected b y transcription driven by the other.