title: Amplification of ssb-1 mutant single-stranded DNA-binding protein in Escherichia coli.
abstract: The ssb-1 gene encoding a mutant Escherichia coli single-stranded DNA-binding protein has been cloned into plasmid pACYC184. The amount of overproduction of the cloned ssb-1 gene is dependent upon its orientation in the plasmid. In the less efficient orientation, 25-fold more mutant protein is produced than in strains carrying only one (chromosomal) copy of the gene; the other orientation results in more than 60-fold overproduction of this protein. Analysis of the effects of overproduction of the ssb-1 encoded protein has shown that most of the deficiencies associated with the ssb-1 mutation when present in single gene copy, including temperature-sensitive conditional lethality and deficiencies in amplified synthesis of RecA protein and ultraviolet light-promoted induction of prophage lambda +, are reversed by increased production of ssb-1 mutant protein. These results provide evidence in vivo that SSB protein plays an active role in recA-dependent processes. Homogenotization of a nearby genetic locus (uvrA) was identified in the cloning of the ssb-1 mutant gene. This observation has implications in the analysis of uvrA- mutant strains and will provide a means of transferring ssb- mutations from plasmids to the chromosome. On a broader scale, the observation may provide the basis of a general strategy to transfer mutations between plasmids and chromosomes.
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics*; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D005784:Gene Amplification; D005798:Genes, Bacterial; D009154:Mutation; D010957:Plasmids; D011938:Rec A Recombinases; D014466:Ultraviolet Rays
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D011938:Rec A Recombinases