Control of replication and gene expression by ADP-ribosylation of DNA in Mycobacterium tuberculosis.

Mycobacterium tuberculosis maintains long-term infections characterised by the need to regulate growth and adapt to contrasting in vivo environments. Here we show that M. tuberculosis complex bacteria utilise reversible ADP-ribosylation of single-stranded DNA as a mechanism to coordinate stationary phase growth with transcriptional adaptation. The DNA modification is controlled by DarT, an ADP-ribosyltransferase, which adds ADP-ribose to thymidine, and DarG, which enzymatically removes this base modification. Using darG-knockdown M. bovis BCG, we map the first DNA ADP-ribosylome from any organism. We show that inhibition of replication by DarT is reversible and accompanied by extensive ADP-ribosylation at the origin of replication (OriC). In addition, we observe ADP-ribosylation across the genome and demonstrate that ADP-ribose-thymidine alters the transcriptional activity of M. tuberculosis RNA polymerase. Furthermore, we demonstrate that during stationary phase, DarT-dependent ADP-ribosylation of M. tuberculosis DNA is required to optimally induce expression of the Zur regulon, including the ESX-3 secretion system and multiple alternative ribosome proteins. Thus, ADP-ribosylation of DNA can provide a mechanistic link through every aspect of DNA biology from replication to transcription to translation.