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.