Variations in the multiple tbp genes in different Halobacterium salinarum strains and their expression during growth.

The presence and expression of the multiple tbp genes encoding TATA-box binding proteins (TBPs) was investigated in various strains and mutants of the archaeon Halobacterium salinarum. Six genes, tbpA through tbpF, are present in the genome of Hbt. salinarum NRC-1 and also in the gas vesicle negative mutant strain R1. The only tbp gene located in the chromosome is tbpE, whereas all others are found in the plasmid DNA. Due to the dynamic nature of the plasmids in the Halobacterium strains, the copy numbers of the alternative tbp genes vary significantly. Five tbp genes (tbpA through tbpE) were present in the wild-type strain Hbt. salinarum PHH1. The tbpC gene of Hbt. salinarum PHH1 carried an ISH27-2 insertion element at the start of the reading frame that prevented the expression. All other tbp genes of PHH1 were expressed under aerobic and anaerobic growth conditions and quantitative RT-PCR yielded tbpE as dominant tbp transcript during the exponential growth phase. The plasmid deletion variant Hbt. salinarum PHH4 lacked all of the tbp genes except for tbpE and showed an altered growth behaviour compared to PHH1 wild-type in the stationary growth phase under anaerobic growth conditions.