Muscle development involves the coordinated regulation of transcription of 
muscle-type-specific genes and their encoded proteins during myogenesis. We show 
here that transcriptional regulation of the Drosophila tropomyosin I (TmI) gene 
during myogenesis is under the control of at least two muscle enhancer regions 
located within the first intron of the gene. Together these enhancer regions 
contain multiple muscle-type-specific positive and negative cis-acting elements 
which together contribute toward full expression of the gene. One of these 
enhancers is contained within a 355-bp fragment that is sufficient to direct 
high levels of temporally regulated expression from a heterologous promoter in 
all muscles of transgenic flies. Dissection of this enhancer region into smaller 
fragments has allowed us to identify a 91-bp enhancer fragment sufficient for 
directing expression in all somatic and visceral muscles of the larva and adult 
but not in the indirect flight muscles and tergal depressor of the trochanter or 
jump muscles of the adult. We also show that this somatic/visceral muscle 
element(s) can be repressed through an adjacent negative control region, 
suggesting that the regulation of expression in these muscles is under dual 
control during both phases of myogenesis. We propose a model in which 
transcriptional regulation of the Drosophila TmI gene is controlled by the 
cooperative interaction of multiple positive and negative cis-acting regulatory 
elements that control the temporal and muscle-type pattern of expression. The 
distribution of enhancer elements and their control of TmI gene expression are 
similar to those regulating transcription of the muscle promoter of the TmII 
gene and provide a framework for the coordinate expression of the two genes.