ANALYSIS OF GAS VESICLE GENE-EXPRESSION IN HALOFERAX-MEDITERRANEI REVEALS THAT GVPA AND GVPC ARE BOTH GAS VESICLE STRUCTURAL PROTEINS

Gas vesicle synthesis in Haloferax mediterranei involves several gene products encoded by a 9.4-kilobase pair DNA region (mc-vac region) tha t contains 13 genes in addition to gvpA encoding the major structural gas vesicle protein. The expression of part of this region, encompassi ng the genes gvpA, gvpC, gvpN, and gvpO was investigated. These genes are transcribed from a common promoter located upstream of gvpA. Trans cripts of 0.34 (gvpA only), 1.8 (gvpA/C), 2.4 (gvpA/C/N) and 3 kilobas es (gvpA/C/N/O) were observed, with the gvpA transcript being the pred ominant mRNA species. The majority of the mRNA formed terminates 64 ba se pairs downstream of gvpA at the cytosine of the sequence 5' TTTTTC 3'. The synthesis of the GvpA and GvpC proteins was investigated by We stern analyses. An antiserum raised against isolated gas vesicles of H f. mediterranei detects, in addition to gas vesicle fragments, the Gvp A protein of the M(r) of approximately 8,000 in lysates derived from d ifferent halobacteria or from Escherichia coli expressing gvpA. In sam ples containing isolated gas vesicles, mainly partially disaggregated gas vesicle fragments hybridize, but a minor amount of monomeric GvpA is also seen. For the detection of the GvpC protein, two versions of t he gvpC gene (full length and gvpDELTAC lacking the 3' part encoding t he acidic C terminus) were expressed in E. coli, and the resulting pro teins were purified. The two antisera raised against these GvpC versio ns indicate the expression of gvpC in different halobacteria. By Weste rn analysis, GvpC is also detectable in samples containing isolated ga s vesicles demonstrating that GvpC is a second, but minor, gas vesicle structural protein.