Description of Osmoregulated Sequences in Haloarchaea
Guadalupe JUEZ*, Consuelo FERRER, Juan C. BOFILL, Francisco J. M. MOJICA, and Francisco RODRIGUEZ-VALERA
Departamento Genetica y Microbiologfa, Universidad Miguel Hernandez, Campus de San Juan, 03080 Alicante, Spain
Response to different salinities in haloarchaea (formerly halobacteria) is poorly understood at the molecular biology level. In order to further clarify some of these aspects we first analyzed the global response to different osmotic conditions in Haloferax volcanii, at both transcriptional (1) and protein synthesis (2) levels. We detected particular proteins/sequences being induced at either low or high salinity conditions, and others responding to both low and high salinity and which could be considered as related to general stress response. A possible overlap between osmotic stress and heat shock response was also observed.
We described (1) the differentially transcribed regions of the H. volcanii genome depending of the salinity of the growth medium. The presence of a large domain within the largest of the megaplasmids (pHV4) with an apparently homogeneous resonse to low salinity was noteworthy (1). In order to identify possible osmoregulated genes some of these regions have been sequenced. Within that particular domain in the pHV4 megaplasmid an ORF has been identified as corresponding to a 900 nt transcript induced under low salinity conditions (as corroborated by primer extension analysis). The predicted protein appears to be a transmembrane protein with several phosphorylation sites. Within the upstream regions we have detected the presence of sequences similar to the HSE and STRE described in Eukaryotes as regulatory elements in the response to heat shock and to different stressing conditions (including osmotic stress). Similar elements have also been detected within the upstream regions of other possible osmoregulated genes within the H. volcanii chromosome. We have noticed the presence of HS-like sequences within the regulatory regions of two different osmoregulated genes from Haloferax mediterranei where we previously described the presence of possible Z- DNA sequences (3), which were partially modified depending of the medium salinity, and for which a possible role in the regulation of gene expression was suggested. Further studies will be of interest to clarify the mechanisms of regulation and genes involved in the response to environmental conditions in this group of extremophles.
1. Ferrer, C., Mojica, F.J.M., Jues, G., and Rodriguez-Valera, F. (1996) J. Bacteriol., 178, 309-313.
2. Mojica, F.J.M., Cisneros, E., Ferrer, C., Rodriguez-Valera, F., and Juez,G. (1997) J. Bacteriol., 179, 5471-5481.
3. Mojica, F.J.M., Juez, G., and Rodriguez-Valera, F. (1993) Mol. Microbiol., 9, 613-621.
