Gas vesicles are intracellular, microbial flotation devices that consist of 
mainly one protein, GvpA. The formation of halobacterial gas vesicles occurs 
along a complex pathway involving 14 different gvp genes that are clustered in a 
genomic region termed the "vac region". Various vac regions found in 
Halobacterium salinarum (p-vac and c-vac), Haloferax mediterranei (mc-vac), and 
Natronobacterium vacuolatum (nv-vac) have been investigated. Except for the 
latter vac region, the arrangement of the gvp genes is identical. Single gvp 
genes have been mutated to study the effect on gas vesicle synthesis in 
transformants and to determine their possible function. Each vac region exhibits 
a characteristic transcription pattern, and regulatory steps have been observed 
at the DNA, RNA, and protein level, indicating a complex regulatory network 
acting during gas vesicle gene expression.