Regulation of the acidic amino acid permease of Aspergillus nidulans.

Chemicals. All chemicals were reagent grade and almost all were obtained from British Drug Houses Ltd, Poole, Dorset. The exceptions were : butyl-PBD [2-(4-tert-butylphenyl)5-(4-biphenylyl)-1, 3,4-oxadiazole] from Koch Light Laboratories Ltd, Colnbrook, Buckinghamshire; malt extract (L 39) and agar no. 3 (L 13) from Oxoid Ltd, London; L-[U-WC]aspartate (227 mCi/mmol), L-[ U-14C]glutamate (I 4.7 mCi/mmol) and ~-[~~S]cyst ine (83 mCi/mmol) from the Radiochemical Centre, Amersham, Buckinghamshire; pacetylpyridine NAD+, L-aspartate, D-glutamate, DL-a-methylglutamate and L-glutamic dehydrogenase (type 11) from Sigma Chemical Company Ltd, London. Preparation and purijication of [35S]~y .s te i~ acid. [35S]Cystei~ acid was prepared from [35S]cystine by the performate oxidation method of Moore (1963). Organism and growth media. A translocation-free, biotin-requiring strain (biI ) (Pontecorvo, Roper, Hemmons, MacDonald & Buften, 1953) of Aspergillus nidulans was used in this work, and was kindly supplied by Dr D. J. Cove, Department of Genetics, University of Cambridge. Stock cultures were maintained on slopes of malt extract (3 %, w/v) solidified with Oxoid agar no. 3 (1.5 o/o, w/v). The medium used for growth of liquid cultures contained (per litre): glucose, I C g; KCl, 0.5 g; MgS0,.7H20, 0.5 g; FeS0,.7H2Q, 0.1 mg; biotin, 0.01 mg. The pH buffer in