Abstract Title: Phosphatidylglycerol and its role in the cell Key words: phosphatidylglycerol, cardiolipin, Barth syndrome, mitochondria, valproate Phosphatidylglycerol (PG) is a minor mitochondrial phospholipid known primarily as a cardiolipin precursor (CL). Accumulation of PG has been observed in the cells of patients with Barth syndrome, a disease characterized by low CL content in mitochondria. Many important findings about this inherited disease come from a study of the yeast model taz1Δ, which, like patients with BTHS, lacks the protein tafazzine needed for CL remodeling. However, unlike human cells, yeast contains PG-specific phospholipase C Pgc1, which prevents the accumulation of PG in these cells. By constructing a double mutant pgc1Δtaz1Δ, we obtained a tool by which we can monitor the effect of elevated PG levels on cellular changes caused by CL deficiency. Our results show that PG accumulation exacerbates taz1Δ mutant defects, making regulation of PG levels one of the factors that may determine the severity of symptoms in patients with BTHS. Subsequently, we focused on verifying the potential of the antiepileptic drug valproate for the treatment of BTHS. Valproate is known to stimulate the CL biosynthetic pathway. In both the yeast and human BTHS cell models, we observed a positive effect of subtherapeutic valproate concentration on their mitochondrial functions.