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Journal of Bacteriology, February 2001, p. 830-834, Vol. 183, No. 3
Department of Microbiology, North Carolina
State University, Raleigh, North Carolina 27695-7615
Received 10 July 2000/Accepted 1 November 2000
Saccharomyces cerevisiae normally will not take up
sterols from the environment under aerobic conditions. A specific
mutant, upc2-1, of the predicted
transcriptional activator UPC2 (YDR213w) has been
recognized as a strain that allows a high level of aerobic sterol
uptake. Another predicted transcriptional activator, the YLR228c gene
product, is highly homologous to Upc2p. In fact, at the carboxy
terminus 130 of the last 139 amino acids are similar between the two
proteins. Since these proteins are very similar, the effect of
mutations in the YLR228c open reading frame (ORF) was compared with
like alterations in UPC2. First, the YLR228c ORF was
insertionally inactivated and crossed with various UPC2 constructs. Deletion of YLR228c and UPC2 in combination
resulted in nonviability, suggesting that the two proteins have some
essential overlapping function. The upc2-1
point mutation responsible for aerobic sterol uptake was duplicated in
the homologous carboxy region of the YLR228c ORF using site-directed
mutagenesis. This mutation on a high-copy vector resulted in an
increase in sterol uptake compared to an isogenic wild-type strain. The
combination of both point mutations resulted in the greatest level of
aerobic sterol uptake. When the YLR228c point mutation was expressed
from a low-copy vector there was little if any effect on sterol uptake. Gas chromatographic analysis of the nonsaponifiable fractions of the
various strains showed that the major sterol for all YLR228c and
UPC2 combinations was ergosterol, the consensus yeast sterol.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.3.830-834.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Identification of a UPC2 Homolog in
Saccharomyces cerevisiae and Its Involvement in Aerobic
Sterol Uptake
*
Corresponding author. Mailing address: Department of
Microbiology, North Carolina State University, Raleigh, NC 27695-7615. Phone: (919) 515-7860. Fax: (919) 515-7867. E-mail:
parks{at}mbio.ncsu.edu.
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