Pp. Davino et al., THE MOLTING HORMONE ECDYSONE IS ABLE TO RECOGNIZE TARGET ELEMENTS COMPOSED OF DIRECT REPEATS, Molecular and cellular endocrinology, 113(1), 1995, pp. 1-9
In Drosophila melanogaster, three temporally distinct ecdysone-respons
ive puff sets, the so-called intermoult, early and late puffs, have be
en described on the salivary gland polytene chromosomes. We have analy
zed in detail a DNA segment of the 3C polytene region, from which orig
inates one of the most prominent intermoult puffs, with the aim of ide
ntifying ecdysone response elements (EcREs). Here we report that two p
utative EcREs of identical sequence are located at this puff site. Int
erestingly, these elements display a novel structural feature, being c
omposed of directly repeated half-sites. Our results show that the EcR
/USP heterodimer known to constitute the ecdysone functional receptor
complex is able to bind to and transactivate through target elements c
omposed of directly repeated half-sites. In addition, we show that the
se elements are also able to bind efficiently USP alone, suggesting th
at USP and EcR/USP could compete for their binding to DNA.