Two separate genes encode the catalytic 70 kDa V-ATPase subunit in Psilotum and Equisetum

Vacuolar type ATPases have been found on various endomembranes of eukaryotic cells, e.g. lysosomes, chromaffin granules, vesicles derived from the Golgi apparatus, endosomes and vacuoles. Although this ATPase type is targeted to different compartments in one cell, only one gene for each subunit had been found per genome. Using PCR across intron-exon boundaries we show that two different genes encode the catalytic subunit of the V-ATPase in Psilotum nudum and Equisetum arvense. The substitution rates for the three codon positions and the intervening sequences show that in Psilotum both genes are transcribed and are under selection pressure, however, this seems not to be the case for Equisetum. The relatively high similarity between the two genes found in each species as compared to the interspecies similarities suggest that for some time after the gene duplication had occurred the two copies were subject to gene conversion mechanisms. An unexpected degree of conservation of the intervening sequences themselves is noted and statistically verified, however, no structural constraints that could explain these findings were detected.