LRPPRC is degraded by LONP1 in the absence of SLIRP and LRPPRC alone cannot preserve mitochondrial transcript stability.

<p>(A) Immunoblotting of SLIRP and LRPPRC protein levels in liver and kidney mitochondria from 12-week old wild-type (<i>Slirp</i>^+/+, <i>Lrpprc</i>^+/+) and <i>Slirp</i> homozygous knockout (<i>Slirp</i>^-/-, <i>Lrpprc</i>^+/+) mice and mice overexpressing <i>Lrpprc</i> on a <i>Slirp</i> homozygous knockout background (Slirp^-/-, Lrpprc^+/T). VDAC was used as a loading control. (B) Immunoblotting of LRPPRC protein levels in <i>Slirp</i>^+/+ and <i>Slirp</i>^-/- primary MEFs after transfection with a siRNA directed against the expression of the LONP1 protease (siLonp1) or with a scrambled siRNA (siCtrl). LONP1 was detected to assess the efficiency of the knockdown (KD), SUV3L1 and PNPT1 were detected to assess the steady-state level of the mitochondrial RNA degradosome and SDHA was used as a loading control (left panel). The right panel represents the quantification of three independent experiments. Error bars represent SEM. * p value < 0.05. *** p value < 0.001. (C) QRT-PCR analysis of the mitochondrial transcript steady-state levels after KD of <i>Lonp1</i> expression in <i>Slirp</i>^+/+ and <i>Slirp</i>^-/- MEFs as described in (B). n = 6. Error bars represent SEM. * p value < 0.05. ** p value < 0.01. *** p value < 0.001. n.s. means not significant.