STUDIES ON THE MECHANISM OF TRANSDUCTION BY BACTERIOPHAGE-PHI-GAMMA .2. FORMATION OF TRANSDUCING ELEMENTS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 95  (3) , 525-544
Abstract
The formation of the transducing elements (TE) of bacteriophage .vphi..gamma., analyzed in lysogens of the thermo-inducible derivative .vphi..gamma.hyI, was found to parallel the formation of plaque-forming particles with a frequency of 2 .times. 10-2 TE-PFU [plaque forming units], but is more sensitive to temperature and to UV. Deletion of 1 of the prophage termini (attR) prevents normal excision and formation of plaque-forming particles, but does not affect the formation of transducing elements, which arise at a rate of nearly 10-1 TE/induced bacterium [Escherichia coli]. Transducing elements would be formed by in situ encapsulation of a hybrid segment from a specific point in the induced prophage, possibly the presumed packaging initiation site of the normal phage genome, before excision of the latter has occurred. Analysis of the mechanism of transduction to partly heterologous lysogens revealed the participation of a coinfecting genome arranged in a linear fashion and gave evidence for a permutation in the sequence of transducing and nontransducing genomes. The data are consistent with a mechanism of encapsidation distinct from the Ter system even for hybrids inheriting part of the .vphi.80 genome, but endowed with the property to form transducing elements like those of .vphi..gamma.. Upon infection, transducing elements are formed after 1 cycle of lytic development with the same characteristics as those resulting from induction, but with a frequency 50-100 times lower. This process is dependent on the efficiency of Int promoted recombination. Superinfection experiments performed under conditions preventing Int promoted recombination reveal that any superinfecting .vphi..gamma. can promote the formation of transducing particles, depending on the presence within the host prophage of a site from which transducing genome packaging initiates.