A DinB Ortholog Enables Mycobacterial Growth under dTTP-Limiting Conditions Induced by the Expression of a Mycobacteriophage-Derived Ribonucleotide Reductase Gene

Mycobacterium species such asM. smegmatis andM. tuberculosis encode at least two translesion synthesis (TLS) polymerases, DinB1 and DinB2, respectively. Although predicted to be linked to DNA repair, their rolein vivo remains enigmatic.M. smegmatis mc2 155, a strain commonly used to investigate mycobacterial genetics, has two copies ofdinB2 , the gene that codes for DinB2, by virtue of a 56-kb chromosomal duplication. Expression of a mycobacteriophage D29 gene (gene 50) encoding a class II ribonucleotide reductase inM. smegmatis ΔDRKIN, a strain derived from mc2 155 in which one copy of the duplication is lost, resulted in DNA replication defects and growth inhibition. The inhibitory effect could be linked to the deficiency of dTTP that resulted under these circumstances. The selective inhibition observed in the ΔDRKIN strain was found to be due solely to a reduced dosage ofdinB2 in this strain.Mycobacterium bovis , which is closely related toM. tuberculosis , the tuberculosis pathogen, was found to be highly susceptible to gene 50 overexpression. Incidentally, these slow-growing pathogens harbor one copy ofdinB2 . The results indicate that the induction of a dTTP-limiting state can lead to growth inhibition in mycobacteria, with the effect being maximum in cells deficient in DinB2.IMPORTANCE Mycobacterium species, such asM. tuberculosis , the tuberculosis pathogen, are known to encode several Y family DNA polymerases, one of which is DinB2, an ortholog of the DNA repair-related protein DinP ofEscherichia coli . Although this protein has been biochemically characterized previously and found to be capable of translesion synthesisin vitro , itsin vivo function remains unknown. Using a novel method to induce dTTP deficiency in mycobacteria, we demonstrate that DinB2 can aid mycobacterial survival under such conditions. Apart from unraveling a specific role for the mycobacterial Y family DNA polymerase DinB2 for the first time, this study also paves the way for the development of drugs that can kill mycobacteria by inducing a dTTP-deficient state.