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J. Bacteriol., 02 1996, 1154-1161, Vol 178, No. 4
S Bass, Q Gu and A Christen
We have isolated three multicopy suppressors of the conditional lethal
phenotype of a prc (tsp) null strain of Escherichia coli. One of these
suppressors included two novel putative protease genes in tandem that map
to 3400 kb or 72.5 centisomes on the chromosome. We propose the names hhoA
and hhoB, for htrA homolog, to denote that these genes encode proteins that
are 58 and 35% identical, respectively, to the HtrA (DegP) serine protease
and 36% identical to each other. The HhoA and HhoB proteins are predicted
to be 455 and 355 amino acids, respectively, in length. The mature HhoA
protein is periplasmic in location, and amino-terminal sequencing shows
that it arises following cleavage of a 27-amino-acid signal peptide.
Searches of the protein and DNA databases reveal a rapidly growing family
of homologous genes in a variety of other bacteria, including several which
are required for virulence in their host. Deletion of the hhoAB genes shows
that they are not required for viability at high temperatures like the
homologous htrA but grow more slowly than wild-type strains. A second
multicopy prc suppressor is the dksA (dnaK suppressor) gene, which is also
a multicopy suppressor of defects in the heat shock genes dnaK, dnaJ, and
grpE. The dksA gene was independently isolated as a multicopy suppressor of
a mukB mutation, which is required for chromosomal partitioning. A third
dosage-dependent prc suppressor includes a truncated rare lipoprotein A
(rlpA) gene.
Copyright © 1996, American Society for Microbiology
Multicopy suppressors of prc mutant Escherichia coli include two HtrA (DegP) protease homologs (HhoAB), DksA, and a truncated R1pA
Department of Molecular Biology, Genentech Inc, South San Francisco, California 94080-4990, USA.
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