TRANSCRIPTION AT DIFFERENT SALINITIES OF HALOFERAX-MEDITERRANEI SEQUENCES ADJACENT TO PARTIALLY MODIFIED PSTI SITES

Two genomic sequences from the halophilic archaeon Haloferax mediterra nei, where we had found PstI restriction-pattern modifications dependi ng on the salinity of the growth medium, have been studied. A markedly salt-dependent differential expression has been detected in the nearb y regions. Two of the open reading frames characterized correspond to two of the differentially expressed transcripts. In both cases the Pst I sites were included in purine-pyrimidine alternancies suggestive of Z-DNA structures and located in non-coding regions with frequent repet itive motifs. A long alternating adenine-thymine tract also appears in the upstream regions of one of these open reading frames. A possible role of local DNA configuration in osmoregulation in this organism is discussed.