The nature of an initiator constitutive mutation in Aspergillus nidulans

Abstract

ONLY a few cis-acting regulatory mutations have been described in eukaryotes. One of these, uap-100, affects the expression of uapA, the adjacent putative structural gene for a uric acid-xanthine permease in the ascomycete Aspergillus nidulans1. Only one protein coded by a formally defined regulatory gene has even been tentatively identified from an eukaryote. This is the positively acting product of the uaY gene of A. nidulans (D. Philippides and C.S., in preparation). As the uapA gene is under the control of uaY (ref. 2 and this paper) the interactions between uap-100 and wild type and mutant uaY products are of considerable interest. Here we show that the constitutivity conferred by uap-100 is strictly dependent on a functional uaY product. This is compelling evidence for the direct involvement of the uaY product in the regulation of uapA and, by implication, of other genes under uaY control, and might indicate that the uaY product exists as at least two conformers in equilibrium.