Transport ATPases play a central role in the bioenergetics of all living cells. In the past we have shown that the F-(eubacterial) and V-type (eukaryotic and archaebacterial) ATPases are very useful molecular markers for early organismal evolution. The proposed research aims to extend the use of the nuclear encoded ATPAse subunits to the early radiation of eukaryotes (especially flagellates and algae) and to the evolution of land plants. Parts of the genes encoding the catalytic subunits of V-type ATPASes will be amplified directly from the genomic or cDNA of various organisms using the polymerase chain reaction (PCR). The obtained sequences will be used to determine the phylogenetic relations between these organisms, including evaluations of the significance of the derived branching patterns.