A transposable element inserted just 5' to a Drosophila glue protein gene alters gene expression and chromatin structure.

The Drosophila Sgs-4 gene directs the developmentally regulated production of a glue protein in the salivary glands of mature larvae. Previous work suggests that Sgs-4 expression requires a remote upstream region that becomes hypersensitive to DNAase I digestion when the gene is active. Here we describe a variant Sgs-4 locus that has a 1.3 kb DNA insert separating the gene from the remote hypersensitive region. This insert defines a new family of transposable elements that we call hobo. Expression from the variant locus is reduced 50 to 100 fold, and rather than the one, normal Sgs-4 transcript, there are now four transcripts, two starting within the hobo element. These multiple transcripts are still expressed only in late larval salivary glands, implying that developmental regulation is unaffected by changes in the site of transcript initiation. When Sgs-4 is active, the remote DNAase I-hypersensitive region, now even more remote due to the insert, still forms over its normal sequences. In contrast, new hypersensitive sites form within hobo near the starts of the new transcripts.