In Saccharomyces cerevisiae, the mitoribosomal RNA of the minor subunit, 15S rRNA, is transcribed as a bicistronic transcript along with tRNA^W. 5′ and 3′ sequences flanking the mature transcript must be removed by cleavage at the respective junctions before incorporating it into the mitoribosome. An in vivo dose–response triphasic system was created to elucidate the role of Ccm1p in the processing of 15S rRNA: Ccm1p supply (“On”), deprivation (“Off”), and resupply (“Back on”). After 72 h under “Off” status, the cells started to exhibit a complete mutant phenotype as assessed by their lack of growth in glycerol medium, while keeping their mitochondrial DNA integrity (ρ⁺). Full functionality of mitochondria was reacquired upon “Back on.” 15S rRNA levels and phenotype followed the Ccm1p intramitochondrial concentrations throughout the “On–Off–Back on” course. Under “Off” status, cells gradually accumulated unprocessed 5′ and 3′ junctions, which reached significant levels at 72–96 h, probably due to a saturation of the mitochondrial degradosome (mtEXO). The Ccm1p/mtEXO mutant (Δccm1/Δdss1) showed a copious accumulation of 15S rRNA primary transcript forms, which were cleaved upon Ccm1p resupply. The gene that codes for the RNA component of RNase P was conserved in wild-type and mutant strains. Our results indicate that Ccm1p is crucial in processing the 15S rRNA primary transcript and does not stabilize the already mature 15S rRNA. Consequently, failure of this function in Δccm1 cells results, as it happens to any other unprocessed primary transcripts, in total degradation of 15S rRNA by mtEXO, whose mechanism of action is discussed.

在酿酒酵母中，次要亚基 15S rRNA 的核糖体 RNA 与 tRNA ^W一起转录为双顺反子转录物。成熟转录物侧翼的 5' 和 3' 序列必须通过在相应连接处的切割去除，然后再将其整合到核糖体中。创建了一个体内剂量反应三相系统来阐明 Ccm1p 在 15S rRNA 处理中的作用：Ccm1p 供应（“开”）、剥夺（“关”）和再补给（“返回”）。在“关闭”状态下 72 小时后，细胞开始表现出完整的突变表型，通过它们在甘油培养基中缺乏生长来评估，同时保持其线粒体 DNA 完整性（ρ ⁺）。线粒体的全部功能在“返回”后重新获得。在整个“On-Off-Back on”过程中，15S rRNA 水平和表型遵循 Ccm1p 线粒体内浓度。在“关闭”状态下，细胞逐渐积累未加工的 5' 和 3' 连接，在 72-96 小时达到显着水平，可能是由于线粒体降解体（mtEXO）的饱和。Ccm1p/mtEXO 突变体 (Δ ccm1 /Δ dss1 ) 显示出 15S rRNA 初级转录形式的大量积累，这些形式在 Ccm1p 再供给时被切割。编码 RNase P 的 RNA 成分的基因在野生型和突变株中是保守的。我们的结果表明 Ccm1p 在处理 15S rRNA 初级转录本中至关重要，并且不会稳定已经成熟的 15S rRNA。因此，这种功能在 Δ ccm1细胞中的失败会导致 15S rRNA 被 mtEXO 完全降解，正如它发生在任何其他未加工的初级转录本上一样，讨论了其作用机制。