INFLUENCE OF SALT ON THE TRANSCRIPTION OF THE GAS-VESICLE GENES OF HALOFERAX-MEDITERRANEI AND IDENTIFICATION OF THE ENDOGENOUS TRANSCRIPTIONAL ACTIVATOR GENE

The transcription of the 14 gvp genes of the gas-vesicle-encoding mc-v ac region was investigated, using RNA from 25% and 15% (w/v) salt cult ures of the moderately halophilic archaeon Haloferax mediterranei. Tra nscription occurred only from two promoters, located in front of the m c-gvpA and mc-gvpD genes. In both cultures transcripts spanning the en tire mc-gvpDEFGHIJKLM transcription unit were formed only during the e xponential growth phase. Amounts of these transcripts were larger in t he 25% salt culture, in which the 2.0 kb mc-gvpD mRNA and large amount s of 1.3 kb and 0.45 kb partial mc-gvpD transcripts were also synthesi zed during the stationary phase. The levels of the mc-gvpD transcripts and of the 324 nt mc-gvpA mRNA increased in parallel during the stati onary phase of the 25% salt culture. Only under these conditions were mRNAs spanning the entire mc-gvpACNO transcription unit observed, and gas-vesicles were formed. Investigation of the influence of the mc-gvp DE genes on both me-vac promoters in transformants revealed that by th emselves they were nearly inactive. The addition of mc-gvpE, however, resulted in a high level of constitutively produced mc-gvpA and mc-gvp D mRNA indicating a transcriptional activator function for the mc-gvpE product.