Ammonium-induced internalisation of UapC, the general purine permease from

Aspergillus nidulans.

Valdez-Taubas J, Harispe L, Scazzocchio C, Gorfinkiel L, Rosa AL.

Departamento de Quimica Biologica, Facultad de Ciencias Quimicas, Universidad

Nacional de Cordoba, Ciudad Universitaria, 5000 Cordoba, Argentina.

jvaldez@mrc-lmb.cam.ac.uk

The Aspergillus nidulans UapC protein is a high-affinity, moderate-capacity,

uric acid-xanthine transporter, which also displays a low transport capacity for

hypoxanthine, adenine, and guanine. It has been previously shown that a

functional UapC-GFP fusion protein localises at the plasma membrane. Here, we

demonstrate that ammonium, a preferred nitrogen source, dramatically changes the

subcellular distribution of UapC. After addition of ammonium, UapC-GFP is

removed from the plasma membrane and is concentrated into the vacuolar

compartment. A chimeric gene construct in which an inducible promoter,

insensitive to nitrogen repression, drives the expression of UapC-GFP, allowed

us to demonstrate that the ammonium-dependent redistribution of UapC can be

dissociated from the transcriptional repression of the gene. These results

provide further support for the occurrence of endocytosis and the

lysosomal-endosomal function of the vacuolar compartment in A. nidulans.