MITOCHONDRIAL INHERITANCE IS DELAYED IN SACCHAROMYCES-CEREVISIAE CELLS LACKING THE SERINE THREONINE PHOSPHATASE PTC1/

In wild-type yeast mitochondrial inheritance occurs early in the cell cycle concomitant with bud emergence. Cells lacking the PTC1 gene init ially produce buds without a mitochondrial compartment; however, these buds later receive part of the mitochondrial network from the mother cell. Thus, the loss of PTC1 causes a delay, but not a complete block, in mitochondrial transport. PTC1 encodes a serine/threonine phosphata se in the high-osmolarity glycerol response (HOG) pathway. The mitocho ndrial inheritance delay in the ptc1 mutant is not attributable to cha nges in intracellular glycerol concentrations or defects in the organi zation of the actin cytoskeleton. Moreover, epistasis experiments with ptc1 Delta and mutations in HOG pathway kinases reveal that PTC1 is n ot acting through the HOG pathway to control the timing of mitochondri al inheritance. Instead, PTC1 may be acting either directly or through a different signaling pathway to affect the mitochondrial transport m achinery in the cell. These studies indicate that the timing of mitoch ondrial transport in wild-type cells is genetically controlled and pro vide new evidence that mitochondrial inheritance does not depend on a physical link between the mitochondrial network and the incipient bud site.