ECDYSTEROID RECEPTOR IN CHIRONOMUS-THUMMI (DIPTERA, CHIRONOMIDAE)

An ecdysteroid receptor protein has been identified and characterized from whole body extracts of Chironomus thummi larvae. The kinetic and physical characteristics of this binding are consistent with the crite ria established for steroid hormone receptors and are similar to those exhibited by the Drosophila ecdysteroid receptor. The binding data of cytosols obtained from different developmental stages (third and four th stage larvae, pupae and adults) indicate only a single type of bind ing site which exists throughout the life cycle of the insect with an average K-d value of 5 x 10(-9) mol/g of protein. Furthermore, single point determinations of the receptor concentration at these stages rev ealed that the receptor level fluctuates. This fluctuation in the rece ptor level corresponds well to the fluctuation in the ecdysteroid tite r indicating that the number of receptors at any particular stage of d evelopment may be regulated by the presence of the moulting hormone.