prlA suppression of defective export of maltose-binding protein in secB mutants of Escherichia coli.
An Escherichia coli strain containing a signal sequence mutation in the periplasmic maltose-binding protein (MBP) (malE18-1) and a point mutation in the soluble export factor SecB (secBL75Q) is completely defective in export of MBP and unable to grow on maltose (Mal- phenotype). We isolated 95 spontaneous Mal+ revertants and characterized them genetically. Three types of extragenic suppressors were identified: informational (missense) suppressors, a bypass suppressor conferring the Mal+ phenotype in the absence of MBP, and suppressors affecting the prlA gene, which encodes a component of the protein export apparatus. In this study, a novel prlA allele, designated prlA1001 and mapping in the putative second transmembrane domain of the PrlA (SecY) protein, was found. In addition, we isolated a mutation designated prlA1024 which is identical to prlA4-2, the mutation responsible for the signal sequence suppression in the prlA4 (prlA4-1 prlA4-2) double mutant (T. Sako and T. Iino, J. Bacteriol. 170:5389-5391, 1988). Comparison of the prlA1024 mutant and the prlA4 double mutant provides a possible explanation for the isolation of these prlA alleles.
Francetić
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O
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
Hanson
M P
MP
Kumamoto
C A
CA
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins / Q000235:genetics*; D002352:Carrier Proteins / Q000378:metabolism*; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D016153:Genes, Suppressor / Q000235:genetics*; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins / Q000235:genetics; D008958:Models, Molecular; D009004:Monosaccharide Transport Proteins; D016296:Mutagenesis; D009154:Mutation; D033902:Periplasmic Binding Proteins; D021382:Protein Sorting Signals / Q000235:genetics; D000069816:SEC Translocation Channels; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA
D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D021382:Protein Sorting Signals; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; C057841:SecY protein, E coli; C461599:maltose transport system, E coli