The gene for a halophilic beta-galactosidase (bgaH) of Haloferax alicanteias a reporter gene for promoter analyses in Halobacterium salinarum

Investigations of transcriptional regulation and the characterization of pr omoters in homologous expression systems are most easily performed using su itable reporter genes. Presumably because of the high internal salt concent ration in halophilic Archaea, the successful application of the commonly us ed reporter genes has not been reported so far. Recently, the gene for an e xtremely halophilic beta-galactosidase (bgaH) from Haloferax alicantei has become available. After transformation of Halobacterium salinarum with a ve ctor-carrying bgaH, the enzyme activity in cell lysates could be readily de termined by a simple colorimetric assay and colonies could be screened for activity on plates containing Xgal substrate. Expression of bgaH under the control of various halobacterial promoters of known strength led to differe nt specific beta-galactosidase activities in the lysates. Using Northern bl ot hybridization and semiquantitative RT-PCR, it was shown that the bgaH tr anscript level corresponded to the specific enzyme activity. Therefore, the bgaH gene of Haloferax alicantei appears to be a useful tool for in vivo s tudies of gene expression in Halobacterium salinarum and possibly other hal ophilic Archaea.