The halophilic archaea Halobacterium salinarum and Haloferax mediterranei produce gas vesicles depending on the growth phase and on environmental factors such as light, salt, or oxygen. Fourteen different gvp genes (gvpACNO and gvpDEFGHIJKLM) are involved in their formation, and the regulation of gvp gene expression occurs at the transcriptional and translational level. Haloferax volcanii offers a clean genetic background for the functional analysis of gas vesicle genes by transformation experiments. Such experiments show that the promoter of the gvpA gene encoding the major gas vesicle structural protein is activated by the endogenous basic leucine-zipper protein GvpE. On the other hand, the GvpD protein, which contains a p-loop motif, is involved either directly or indirectly in the repression of the gvpA promoter activity. Eight of the fourteen p-gvp genes (p-gvpAO and p-gvpFGJKLM) enable gas vesicle formation in Hf. volcanii transformants and thus constitute the minimal p-vac region.