The DinG exonuclease acts as a primary quality controller to remove unprocessed ribosomal RNAs

Bacteria lacking DEAD-box RNA-helicases often show reduced growth and aberrant maturation of ribosomal subunits resulting in fewer active ribosomes. Here, we show that the slow growth observed in a strain lacking the RNA-helicase CshC in the bacterial pathogen Listeria monocytogenes can be suppressed by mutations in the exonuclease DinG. A strain lacking both CshC and DinG increased the number of mature and active ribosomes compared to the parental ΔcshC mutant. DinG acts as a 3'- to 5'-exoribonuclease, targeting immature, unprocessed ribosomal RNA in vitro and in vivo while leaving processed rRNA undisturbed. In addition, DinG directly or indirectly interferes with the ribonuclease M5 mediated pre-5S rRNA processing. We suggest that DinG acts as a primary ribosome quality control ribonuclease that initiates degradation of unprocessed rRNA.