THE GVPA/C CLUSTER OF ANABAENA-FLOS-AQUAE HAS MULTIPLE COPIES OF A GENE ENCODING GVPA

Southern analysis of genomic DNA from Anabaena flos-aquae revealed that the genes encoding the two authenticated protein components of cyanobacterial gas vesicles, GvpA and GvpC, were carried on the same 4.9-kb NindIII restriction fragment. By comparing the hybridization intensities observed when either gvpA- or gvpC-specific oligonucleotides are bound to this HindIII fragment, we calculated that the A. flos-aquae genome contains seven copies of gvpA and a single copy of gvpC. The nucleotide sequence of the longest cloned section of the gvpA/C cluster of A. flos-aquae DNA revealed the presence of four complete copies of gvpA and part of a fifth copy located upstream from a single copy of gvpC; no clones carrying the entire gvpA/C-bearing HindIII fragment were identified. The distribution of Sau3A restriction sites throughout the gvpA/C-bearing genomic HindIII fragment resembled that seen in the cloned portion of the gvpA/C cluster and is consistent with that expected for a cluster containing seven copies of gvpA and one copy of gvpC. The length of transcripts that hybridize to both gvpA and gvpC on Northern blots was consistent with a 7 gvpA + 1 gvpC transcriptional unit.