The initiator element of the Drosophila β2 tubulin gene core promoter contributes to gene expression in vivo but is not required for male germ-cell specific expression

The tissue-specific expression of the Drosophila β2 tubulin gene (B2t) is accomplished by the action of a 14-bp activator element (β2UE1) in combination with certain regulatory elements of the TATA-less, Inr-containing B2t core promoter. We performed an in vivo analysis of the Inr element function in the B2t core promoter using a transgenic approach. Our experiments demonstrate that the Inr element acts as a functional cis-regulatory element in vivo and quantitatively regulates tissue-specific reporter expression in transgenic animals. However, our mutational analysis of the Inr element demonstrates no essential role of the Inr in mediating tissue specificity of the B2t promoter. In addition, a downstream element seems to affect promoter activity in combination with the Inr. In summary, our data show for the first time the functionality of the Inr element in an in vivo background situation in Drosophila.