Filamentous phage DNA cloning vectors: A noninfective mutant nonh a nonpolar deletion in gene III

Abstract

A filamentous phage derivative, fKN16, has been constructed from the tetracyclineresistance transducing phage fd-tet by deleting a 507-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 less than 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. And indeed, 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 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 λ DNA as model foreign DNA. fKN16 may also be useful in studying the role of the gene III protein in the filamentous phage life cycle.