Role of Rmd9p in 3′-end processing of mitochondrial 15S rRNA in Saccharomyces cerevisiae

Ribosome biogenesis, involving processing/assembly of rRNAs and r-proteins is a vital process. In Saccharomyces cerevisiae mitochondria, ribosomal small subunit comprises 15S rRNA (15S). While the 15S 5′-end processing uses Ccm1p and Pet127p, the mechanisms of the 3′-end processing remain unclear. We reveal involvement of Rmd9p in safeguarding/processing 15S 3′-end. Rmd9p deficiency results in a cleavage at a position 183 nucleotides upstream of 15S 3′-end, and in the loss of the 3′-minor domain. Rmd9p binds to the sequences in the 3'-end region of 15S, and a genetic interaction between rmd9 and dss1 indicates that Rmd9p regulates/limits mtEXO activity during the 3′-end spacer processing.