Further sequence requirements for male germ cell-specific expression under the control of the 14 bp promoter element (beta 2UE1) of the Drosophila beta 2 tubulin gene.

We have investigated a 14 bp promoter element (beta 2UE1) that is required for testis-specific expression of the Drosophila beta 2 tubulin gene. To further elucidate the role of the 14 bp element, we fused different promoter constructs to the E. coli lacZ gene and established transgenic strains with the aid of the Drosophila P-element transformation system. Germ line transformation experiments with constructs in which the element in the beta 2 tubulin gene promoter was exchanged for a related sequence from the promoter region of the Drosophila beta 3 tubulin gene led to a dramatic reduction in the expression of the lacZ gene in the testis. Exchanging the 14 bp promoter element for a similar sequence from the distal promoter of the Drosophila alcohol dehydrogenase gene abolished expression. This might indicate that the sequence differences between the beta 2UE1 and the beta 2UE1-related elements reflect functional differences between these elements. Constructs in which the beta 2UE1 was fused to the hsp70 promoter revealed that testis-specific expression of a marker gene is obtained only when the element is located at the correct distance from the transcription initiation site. However, constructs in which the beta 2UE1 was inserted at about the correct position (between -41 and -54 bp) upstream of a truncated beta 3 tubulin gene promoter did not show any expression. By making beta 2-beta 3 gene promoter fusions it was found that both the region surrounding the beta 3 transcription initiation site as well as the first 116 b of beta 3 leader sequences independently reduce testis-specific expression. These findings suggest that the testis-specific expression of the Drosophila beta 2 tubulin gene underlies a unique regulatory mechanism.