5'-flanking sequence required for regulated expression of a muscle-specific Drosophila melanogaster actin gene.

We have functionally tested derivatives of a muscle-specific Drosophila melanogaster actin gene in which 5'-flanking sequences have been deleted or rearranged. From our results we conclude that approximately 1,000 nucleotides of 5'-flanking sequence are required for wild-type levels of mRNA accumulation during flight muscle development. Derivatives having 875 or 865 nucleotides of upstream sequence could be expressed normally, but were prone to influence by flanking foreign DNA sequences. Derivatives retaining 600 or fewer nucleotides of flanking DNA did not direct detectable levels of mRNA accumulation. The sequence residing between -919 and -640 could be inverted and yet retain normal function. Deletion of this sequence reduced mRNA accumulation markedly, but did not affect its spatial localization, suggesting that elements which confer tissue specificity reside close to the point of transcription initiation.