Iron-stress-induced-A proteins (IsiAs) are expressed in cyanobacteria under iron-deficient conditions, and surround photosystem I (PSI) trimer with a ring formation. A cyanobacterium Anabaena sp. PCC 7120 has four isiA genes; however, it is unknown how the IsiAs are associated with PSI. Here we report on molecular organizations and function of the IsiAs in this cyanobacterium. A deletion mutant of the isiA1 gene was constructed, and the four types of thylakoids were prepared from the wild-type (WT) and ΔisiA1 cells under iron-replete (+Fe) and iron-deficient (−Fe) conditions. Immunoblotting analysis exhibits a clear expression of the IsiA1 in the WT−Fe. The PSI-IsiA1 supercomplex is found in the WT−Fe, and excitation-energy transfer from IsiA1 to PSI is verified by time-resolved fluorescence analyses. Instead of the IsiA1, both IsiA2 and IsiA3 are bound to PSI monomer in the ΔisiA1−Fe. These findings provide insights into multiple-expression system of the IsiA family in this cyanobacterium.

铁胁迫诱导的A蛋白（IsiAs）在缺铁条件下在蓝细菌中表达，并围绕光系统I（PSI）三聚体形成环。蓝藻鱼腥藻 PCC 7120具有四个isiA基因。但是，尚不清楚IsiA如何与PSI相关联。在这里，我们报道了这种蓝细菌中IsiA的分子组织和功能。构建了一个isiA1基因的缺失突变体，并从野生型（WT）和ΔisiA1制备了四种类囊体富铁（+ Fe）和缺铁（-Fe）条件下的细胞。免疫印迹分析显示WT-Fe中IsiA1的表达清晰。在WT-Fe中发现了PSI-IsiA1超复合物，并且通过时间分辨荧光分析验证了从IsiA1到PSI的激发能转移。代替IsiA1，IsiA2和IsiA3都结合在ΔisiA1 -Fe中的PSI单体上。这些发现为该蓝细菌中的IsiA家族的多重表达系统提供了见识。