Molecular and General Genetics MGG

, Volume 218, Issue 2, pp 183–189

Involvement of DnaK protein in mini-F plasmid replication: Temperature-sensitive seg mutations are located in the dnaK gene

Authors

  • Bunichi Ezaki
    • Department of Molecular Genetics, Institute for Medical GeneticsKumamoto University Medical School
  • Teru Ogura
    • Department of Molecular Genetics, Institute for Medical GeneticsKumamoto University Medical School
  • Hirotada Mori
    • Department of Molecular Genetics, Institute for Medical GeneticsKumamoto University Medical School
  • Hironori Niki
    • Department of Molecular Genetics, Institute for Medical GeneticsKumamoto University Medical School
  • Sota Hiraga
    • Department of Molecular Genetics, Institute for Medical GeneticsKumamoto University Medical School
Article

DOI: 10.1007/BF00331267

Cite this article as:
Ezaki, B., Ogura, T., Mori, H. et al. Molec Gen Genet (1989) 218: 183. doi:10.1007/BF00331267

Summary

The seg mutants (seg-1 and seg-2) of Escherichia coli cannot support the replication of the F factor and mini-F plasmids at 42°C. We cloned the wild-type E. coli chromosomal DNA fragment complementing the seg-1 and seg-2 mutations and found that both mutations were complemented by the wild-type dnaK gene coding for a heat shock protein. Transduction with phage P1 indicated that the seg-2 mutation is located at about 0.3 min in the region containing the dnaK gene in the order trpR-thrA-seg-2-leuB, consistent with the locus of the dnaK gene. Cloning and sequencing of the dnaK gene of the seg mutants showed that there was one base substitution within the dnaK gene in each mutant causing an amino acid substitution. These results indicate that the seg gene in which the seg-1 and seg-2 mutations occurred is identical to the dnaK gene. The mini-F plasmid pXX325 did not transform a dnaK null mutant to ampicillin resistance at 30°C in contrast to plasmids pBR322, pACYC184 and pSC101, which did. The active dnaK (seg) gene product is therefore essential for replication of the mini-F plasmid at both 30° and 42°C.

Key words

dnaK gene seg mutations F plasmid Replication

Copyright information

© Springer-Verlag 1989