msachs at ADMIN.OGI.EDU
Wed Jun 28 13:35:46 EST 1995
Z. Luo, M. Freitag and M. S. Sachs (Mol.Cell. Biol., in press).
Translational regulation in response to changes in amino acid availability
in Neurospora crassa.
We examined the regulation of Neurospora crassa arg-2 and cpc-1 in response
to amino acid availability. arg-2 encodes the small subunit of
arginine-specific carbamoyl phosphate synthetase; it is subject to unique
negative regulation by Arg and is positively regulated in response to
limitation for many different amino acids through a mechanism known as
cross-pathway control. cpc-1 specifies a transcriptional activator
important for cross-pathway control. Expression of these genes was
compared to that of the cytochrome oxidase subunit V gene, cox-5. Analyses
of mRNA levels, polypeptide pulse labeling results and the distribution of
mRNA in polysomes indicated that Arg-specific negative regulation of arg-2
affected both the levels of arg-2 mRNA and arg-2 mRNA translation.
Negative translational effects on arg-2 and positive translational effects
on cpc-1 were apparent soon after cells were provided with exogenous Arg.
In cells limited for His, increased expression of arg-2 and cpc-1, and
decreased expression of cox-5, also had translational and transcriptional
components. The arg-2 and cpc-1 transcripts contain upstream open reading
frames (uORFs), as do their Saccharomyces cerevisiae homologs CPA1 and
GCN4. We examined the regulation of arg-2-lacZ reporter genes containing
or lacking the uORF start codon; the capacity for arg-2 uORF translation
appeared critical for controlling gene expression.
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