Molecular characterization of idiA and adjacent genes in the cyanobacteriaSynechococcus sp strains PCC 6301 and PCC 7942

IdiA ((i) under bar ron-(d) under bar eficiency-<(i)under bar>nduced protei n (A) under bar) is a protein expressed at highly elevated levels in Synech ococcus sp. strains PCC 6301 and PCC 7942 under Fe or Mn-limiting growth co nditions. Besides being similar to two bacterial Fe-binding proteins, SfuA and FbpA, IdiA shows similarity to two ORFs (slr0513 and slr1295) of Synech ocystis sp. PCC 6803. Northern blot analysis detected one transcript of abo ut 1300 nt in RNA extracted from Synechococcus sp. PCC 6301 and PCC 7942 gr own under Fe deficiency. The intensity of this transcript was considerably reduced in Fe-sufficient culture. It could be further shown that the regula tion of IdiA expression is at the transcriptional level and that transcript ion and translation of IdiA are closely linked. Primer extension analysis i ndicated a single transcriptional start site 193 nt upstream of the first p resumed translational start codon. Moreover. molecular characterization of the entire 5.8 kb chromosomal HindIII DNA fragment carrying the idiA gene f rom Synechococcus sp. PCC 6301 led to the identification of six long ORFs i n addition to idiA. The two genes adjacent to idiA, and dpsA located 2018 n t downstream of idiA, were insertionally inactivated in Synechococcus sp. P CC 7942 and the corresponding mutants were partially characterized. These e xperiments provide evidence that the gene products of idiB, located immedia tely downstream of idiA, and of dpsA are involved in the activation of IdiA expression, since the absence of each of these two gene products prevents the greatly elevated expression of IdiA under nutrient deficiency.