TY - JOUR
T1 - The Escherichia coli SeqA protein destabilizes mutant DnaA204 protein
AU - Torheim, N K
AU - Boye, E
AU - Løbner-Olesen, A
AU - Stokke, T
AU - Skarstad, K
PY - 2000/8
Y1 - 2000/8
N2 - In wild-type Escherichia coli cells, initiation of DNA replication is tightly coupled to cell growth. In slowly growing dnaA204 (Ts) mutant cells, the cell mass at initiation and its variability is increased two- to threefold relative to wild type. Here, we show that the DnaA protein concentration was two- to threefold lower in the dnaA204 mutant compared with the wild-type strain. The reason for the DnaA protein deficiency was found to be a rapid degradation of the mutant protein. Absence of SeqA protein stabilized the DnaA204 protein, increased the DnaA protein concentration and normalized the initiation mass in the dnaA204 mutant cells. During rapid growth, the dnaA204 mutant displayed cell cycle parameters similar to wild-type cells as well as a normal DnaA protein concentration, even though the DnaA204 protein was highly unstable. Apparently, the increased DnaA protein synthesis compensated for the protein degradation under these growth conditions, in which the doubling time was of the same order of magnitude as the half-life of the protein. Our results suggest that the DnaA204 protein has essentially wild-type activity at permissive temperature but, as a result of instability, the protein is present at lower concentration under certain growth conditions. The basis for the stabilization in the absence of SeqA is not known. We suggest that the formation of stable DnaA-DNA complexes is enhanced in the absence of SeqA, thereby protecting the DnaA protein from degradation.
AB - In wild-type Escherichia coli cells, initiation of DNA replication is tightly coupled to cell growth. In slowly growing dnaA204 (Ts) mutant cells, the cell mass at initiation and its variability is increased two- to threefold relative to wild type. Here, we show that the DnaA protein concentration was two- to threefold lower in the dnaA204 mutant compared with the wild-type strain. The reason for the DnaA protein deficiency was found to be a rapid degradation of the mutant protein. Absence of SeqA protein stabilized the DnaA204 protein, increased the DnaA protein concentration and normalized the initiation mass in the dnaA204 mutant cells. During rapid growth, the dnaA204 mutant displayed cell cycle parameters similar to wild-type cells as well as a normal DnaA protein concentration, even though the DnaA204 protein was highly unstable. Apparently, the increased DnaA protein synthesis compensated for the protein degradation under these growth conditions, in which the doubling time was of the same order of magnitude as the half-life of the protein. Our results suggest that the DnaA204 protein has essentially wild-type activity at permissive temperature but, as a result of instability, the protein is present at lower concentration under certain growth conditions. The basis for the stabilization in the absence of SeqA is not known. We suggest that the formation of stable DnaA-DNA complexes is enhanced in the absence of SeqA, thereby protecting the DnaA protein from degradation.
KW - Bacterial Outer Membrane Proteins
KW - Bacterial Proteins/genetics
KW - DNA Replication
KW - DNA, Bacterial/genetics
KW - DNA-Binding Proteins/genetics
KW - Escherichia coli/genetics
KW - Escherichia coli Proteins
KW - Gene Expression Regulation, Bacterial
KW - Mutation
KW - Transcription Factors
M3 - Journal article
C2 - 10931356
SN - 0950-382X
VL - 37
SP - 629
EP - 638
JO - Molecular Microbiology
JF - Molecular Microbiology
IS - 3
ER -