Cloning and expression of the flagellar hook gene on hybrid plasmids in minicells

SPECIFIC Escherichia coli DNA fragments carrying flagellar genes have been cloned on λ vehicles and gene expression has been studied in λ-infected ultraviolet irradiated-cells1,2. This work has led to the identification of several gene products involved in flagellar function. But, the structural gene for the hook subunit protein, which is one of the major flagellar components has not been identified. This gene could have been missed if it was not part of the DNA that was cloned, if it was cleaved during endonuclease treatment or if it was transcribed at such a low level that the product could not be detected in ultraviolet-irradiated cells. We report here another approach which avoids these difficulties and has enabled us to identify the region of the genome which carries genes involved in the synthesis of flagellar hook and basal structures. This result is interesting for two reasons. First, it demonstrates the general applicability of cloning techniques to the identification of any gene product in E. coli. Second, it focuses attention on a hitherto poorly defined group of genes involved in flagellar structure and function.