Superinfection immunity of mycobacteriophage L5: applications for genetic transformation of mycobacteria

Mycobacteriophage L5 is a temperate phage of the mycobacteria that forms stable lysogens in Mycobacterium smegmatis. We show here that the 183‐amino‐acid product of L5 gene 71 confers immunity to L5 superinfection, is required for maintenance of the lysogenic state and contains a helix‐turn‐helix DNA‐binding motif—properties associated with repressors of temperate phages. We have utilized these observations to demonstrate the use of L5 gene 71 as a selectable marker for genetic transformation of the mycobacteria. Significantly, the use of L5 gene 71 as a selectable gene avoids the requirement for antibiotic‐resistance genes providing an important tool for manipulation of the pathogens Mycobacterium tuberculosis and Mycobacterium avium, and for the construction of recombinant BCG vaccines. Copyright © 1993, Wiley Blackwell. All rights reserved