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.


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.