FILAMENTOUS PHAGE DNA CLONING VECTORS - A NON-INFECTIVE MUTANT WITH A NON-POLAR DELETION IN GENE-III

A filamentous phage derivative, fKN16, was constructed from the tetracycline-resistance transducing phage fd-tet by deleting a 50 base-pair (bp) segment of phage gene III. In accord with the importance of the gene III protein in infection, the infectivity of fKN16 phage is < 10-8 that of fd-tet phage. In contrast to most gene III amber mutants, which are polar on the downstream phage genes VI and I, fKN16 should be a nonpolar mutant since its 507 bp deletion spans an integral number of coding triplets. Two phage traits that may depend on gene VI and I function, the level of phage production and packaging into unit-length virions, appear to be normal in fKN16. High phage production coupled with very low infectivity [Escherichia coli] make fKN16 suitable as a vector for DNA cloning experiments requiring a high level of biological containment. The characteristics of fKN16 as a vector were investigated in detail, using HindIII fragments of phage .lambda. DNA as model foreign DNA. fKN16 may be useful in studying the role of the gene III protein in the filamentous phage life cycle.