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Genetic analysis of F sex factor cistrons needed for surface exclusion in Escherichia coli

1980; Elsevier BV; Volume: 138; Issue: 4 Linguagem: Inglês

10.1016/0022-2836(80)90065-0

1089-8638

Mark Achtman, Paul A. Manning, Barica Kušećek, Sybille Schwuchow, W. Kowall Neil,

DNA and Nucleic Acid Chemistry

The structural genes of the F plasmid which encode surface exclusion have previously been cloned in the vector plasmid pSC101 to yield the chimeric plasmid pRS31. Point mutations which partially inactivate surface exclusion have been generated in pRS31 by in vitro mutagenesis. These mutations have been used to demonstrate that two independent cistrons, traS and traT, each encodes only one of the two aspects of the surface exclusion phenomenon. When these mutations were moved genetically to Flac, they affected surface exclusion but did not affect either the synthesis of F pili or the ability to act as a donor in conjugation. 60 mutants of Flac were isolated which were either totally or only partially defective in producing surface exclusion. Those mutants which were only partially defective carried either traS or traT mutations. Most of the other mutations were in the traJ cistron, which is involved in transcriptional regulation of the tra operon. These latter mutants were defective in F piliation and in DNA transfer as well. Still other mutants carried mutations which were polar on the surface exclusion cistrons or carried multiple mutations. These results demonstrate that the F plasmid contains two structural cistrons for surface exclusion and one cistron which is involved in transcriptional regulation.