A Path from Mitochondria to the Yeast Nucleus

We have identified a path in yeast, from mitochondria to the nucleus, which may have a regulatory function in mitochondrial biogenesis. This path is evident as an elevated expression of a number of nuclear DNA sequences in response to specific defects in the mitochondrial genome, including the absence of mitochondrial DNA in ρ^0 petites. Among those nuclear sequences preferentially expressed in certain respiratory-deficient cells are stable poly (A)^+ transcripts derived from the so-called non-transcribed spacer region of the nuclear ribosomal DNA repeat, where they are most abundant in the ρ^0 petite. Although the function of these unusual RNAs is unclear, the observations may reflect the presence of a mitochondrial homeostatic control system in yeast, which we suggest could function to adjust the mass of mitochondria and mitochondrial DNA in the cell in response to inequities in organelle apportionment during cell budding.