Actin
Cytoskeleton Is Required For Nuclear Localization Of Gln3 During Nitrogen
Limitation in Saccharomyces cerevisiae.
Kathleen H. Cox,
Jennifer J. Tate, Terrance G. Cooper
Molecular Sciences, University of Tennessee, 858 Madison Ave., Memphis, TN
38163, USA (khcox@utmem.edu)
S. cerevisiae selectively utilizes good
nitrogen sources (gln) in preference to poor ones (pro), by down-regulating
transcription of the genes encoding proteins that transport and degrade poor
nitrogen sources when excess nitrogen is available, Nitrogen Catabolite
Repression (NCR). Rapamycin inhibition of Tor1/2 mimics the cellular response
to limiting nitrogen and has implicated this signal transduction pathway in
NCR. When cells are shifted from a good to a poor nitrogen source, Gln3 (an
NCR-sensitive transcription activator) moves from the cytoplasm into the
nucleus. It returns to the cytoplasm when cells are returned to a good nitrogen
source. We have demonstrated Gln3 is not uniformly distributed in the cytoplasm
(J. Biol. Chem. 277:37559). Such non-uniform distribution could result from a
variety of interactions including association with a cytoplasmic vesicular
system or components of the cytoskeleton. We used latrunculin, a drug that
inhibits actin polymerization, to determine whether the actin cytoskeleton
participates in intracellular Gln3 movement. Latrunculin-treatment prevents
nuclear accumulation of Gln3 and NCR-sensitive transcription in cells shifted
from ammonia to pro medium. In contrast, latrunculin does not prevent
cytoplasmic Gln3 accumulation when cells are shifted from pro to gln medium.
These data suggest the actin cytoskeleton is required for nuclear entry of Gln3
in response to limiting nitrogen. Supported by NIH grant GM-35642.