Cloning,
Expression of the Abrin-a A-chain in Escherichia coli and Measurement of
the Biological Activities in vitro
ZHOU Zhou, LIU Hao-Ping1, CHEN
Jiang-Ye*
( State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell
Biology,
Shanghai Institutes for Biological Sciences, the Chinese Academy of Sciences,
Shanghai 200031, China;
1Department of Biological Chemistry, College of Medicine, University
of California, Irvine, Irvine, California 92697-1700, USA )
Abstract The
pathogenic fungus Candida albicans has a dimorphic transition
in various environmental conditions. Many regulatory factors and several
transduction pathways have been identified in controlling filamentous growth. G1
cyclins Cln1 and Cln2 have been reported as involved in the control of
morphogenesis in Saccharomyces cerevisiae. Diploid cln1/cln1
and cln2/cln2 strains completely lost the
ability to form pseudohyphae. A C. albicans genomic DNA
library was introduced into cln1/cln1 and cln2/cln2
mutants to screen genes which could complement its filamentous growth defect.
In this screening a BEM1 homolog, CaBEM1, was
identified. The CaBEM1 gene has an ORF of 1 899 bp, encoding a
putative protein of 632 amino acids. The CaBem1 protein shares highest homology
in amino acids with Bem1 (38%) of S. cerevisiae and Scd2 (32%)
of Schizosaccharomyces pombe. Sequence analysis showed that
the CaBem1 contains two N-terminal SH3 domains, a PX domain and a C-terminal
PB1 domain. It is believed these domains are required for binding to proteins
involved in polarized growth in S. cerevisiae and S.
pombe. Ectopic expression of the CaBEM1 gene in
diploid S. cerevisiae suppressed defects in filamentous growth
of some mutants under nitrogen starvation conditions. This suppression bypassed
MAPK pathway and cAMP/PKA pathway in filamentous growth. These results suggest
that the CaBem1 protein may be a downstream component of these two signal
transduction pathways of filament formation.
Key words Candida albicans; CaBEM1;filamentous growth
*Corresponding author: Tel,
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