Abstract
The region from 1.4 to 2.7 kb upstream of Drosophila melanogaster gene Sgs-3 is responsible for a 10-fold increase in Sgs-3 transcript levels in the third instar larval salivary gland. This region includes the related Sgs-7 gene from the 68C glue gene cluster as well as 400 bp of its 5' sequences. We show that two elements are involved, each contributing a modest 3-fold effect. One of these includes Sgs-7 transcribed sequences some 2.3 kb upstream of Sgs-3, although Sgs-7 transcription is not involved. Although important for the overall levels of Sgs-3 expression, they are clearly not strong, viral-like enhancer elements. We propose that many position effects observed in P element transformation studies are the consequence of insertion in the vicinity of similar elements dispersed throughout the genome and having modest effects on transcript levels.