MAPA, AN IRON-REGULATED, CYTOPLASMIC MEMBRANE-PROTEIN IN THE CYANOBACTERIUM SYNECHOCOCCUS SP STRAIN PCC7942

Growth of Synechococcus sp. strain PCC 7942 in iron-deficient media le ads to the accumulation of an similar to 34-kDa protein. The gene enco ding this protein, mapA (membrane-associated protein A), has been clon ed and sequenced (GenBank accession number, L01621). The mapA transcri pt is not detectable in normally grown cultures but is stably accumula ted by cells grown in iron-deficient media. However, the promoter sequ ence for this gene does not resemble other bacterial iron-regulated pr omoters described to date. The carboxyl-terminal region of the derived amino acid sequence of MapA resembles bacterial proteins involved in iron acquisition, whereas the amino-terminal end of MapA has a high de gree of amino acid identity with the abundant, chloroplast envelope pr otein E37. An approach employing improved cellular fractionation techn iques as well as electron microscopy and immunocytochemistry was essen tial in localizing MapA protein to the cytoplasmic membrane of Synecho coccus sp. strain PCC 7942. When these cells were grown under iron-def icient conditions, a significant fraction of MapA could also be locali zed to the thylakoid membranes.