Expression of a Pho85 cyclin-dependent kinase is repressed during the
dimorphic transition in Sporothrix schenckii
Marisol de Jes
uus-Berr
ııos
*
and Nuri Rodr
ııguez-del Valle
Department of Microbiology and Medical Zoology, Medical Sciences Campus, University of Puerto Rico, San Juan 00936, USA
Received 24 September 2001; accepted 22 April 2002
Abstract
Sporothrix schenckii is a pathogenic fungus that undergoes a dimorphic transition from yeast to mycelium in response to en-
vironmental conditions such as cell density, temperature, and calcium. We identified a homolog of the Pho85 cyclin-dependent
kinase (Cdk) that mediates cellular responses to environmental conditions in other organisms. By Western blot, three proteins
containing the PSTAIRE motif, which characterize the cyclin-dependent protein kinases, were identified in S. schenckii. The gene
encoding a Pho85 homolog, PhoSs, was identified and sequenced. The phoSs gene consists of 990 bp, contains one intron, and
encodes a protein of 306 amino acids. The S. schenckii Pho85 homolog shares features with Cdks, including the PSTAIRE motif, an
ATP binding domain, and a serine–threonine kinase domain. By quantitative competitive RT-PCR, expression of the phoSs gene
was found to decrease 30-fold during the yeast to mycelium transition. The addition of extracellular calcium accelerated the di-
morphic transition and restored phoSs expression. These findings suggest PhoSs may participate in the control of the yeast to
mycelium transition in S. schenckii. Ó 2002 Elsevier Science (USA). All rights reserved.
Keywords: Sporothrix schenckii; PhoSs; Pho85; Cyclin-dependent kinase
1. Introduction
Cyclin-dependent kinases (Cdks) are key regulators
of cell cycle progression. Cdks consist of a catalytic
subunit and an associated cyclin activator (Gao and
Zelenka, 1997; Rousel, 2000). The Cdk catalytic kinase
subunits are highly conserved and consist of 250–300
amino acids (30–40 kDa) (Moffat et al., 2000; Morgan,
1997). The first Cdks identified were the products of the
cdc2 gene (p34
cdc2
) in the fission yeast Schizosacchar-
omyces pombe and the CDC28 gene in the budding yeast
Saccharomyces cerevisiae (Morgan, 1997). In S. cerevi-
siae, a single Cdk mediates diverse cell cycle transitions
by associating with multiple stage specific cyclins
(Morgan, 1997).
Although many Cdks function directly in cell cycle
progression, some Cdks control other cellular processes
including gene expression (reviewed by Cross, 1995;
Lenburg and O’Shea, 1996; Nigg, 1996; O’Neill and
O’Shea, 1995). One example is the Pho85 Cdk in S. ce-
revisiae (Toh-e et al., 1988). Pho85 was originally iden-
tified as a regulator of phosphate metabolism (Lenburg
and O’Shea, 1996; Uesono et al., 1987), although it can
function\ in G1 progression in the absence of the G1
cyclins, Cln1, and Cln2, that normally activate Ccd28
(Espinoza et al., 1994; Measday et al., 1994). Pho85 also
plays a role in modulating the transcriptional response
to nutritional signals in S. cerevisiae. When yeast cells
are grown under high-phosphate conditions, Pho85 as-
sociates with the cyclin Pho80 and represses expression
of the gene encoding the secreted acid phosphatase Pho5
(Lenburg and O’Shea, 1996).
By binding to different cyclins, Pho85 has been shown
to regulate diverse processes such as glycogen metabo-
lism, amino acid biosynthesis, actin regulation, and cell
cycle progression in S. cerevisiae (Andrews and Maesdy,
1998; Meimoun et al., 2000; Moffat et al., 2000). pho85
mutants exhibit constitutive acid phosphatase produc-
tion, a slow growth rate on glucose, a failure to utilize
Fungal Genetics and Biology 37 (2002) 39–48
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*
Corresponding author. Present address: Box 3546, 322 CARL
Bldg., Research Dr., Duke University Medical Center, Durham, NC
27710, USA. Fax: +919-684-5458.
E-mail address: dejesus@duke.edu (M. de Jes
uus-Berr
ııos).
1087-1845/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved.
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