CHARACTERIZATION OF DEVA, A GENE REQUIRED FOR THE MATURATION OF PROHETEROCYSTS IN THE CYANOBACTERIUM ANABAENA SP STRAIN PCC-7120

Mutant M7, obtained by transposon mutagenesis of the cyanobacterium An abaena sp. strain PCC 7120, is impaired in the development of mature h eterocysts. Under aerobic conditions, the mutant is unable to fix N-2 because of a deficiency of at least mo components of the oxygen-protec tive mechanisms: a hemoprotein-coupled oxidative reaction and heterocy st specific glycolipids. DNA contiguous with the inserted transposon w as recovered from the mutant and sequenced. The transposon had inserte d itself within a 732-bp open reading frame designated devA. The wild- type form of devA, obtained from a lambda-EMBL3 library of Anabaena sp . DNA, had the identical sequence. Directed mutagenesis of devA in the wild-type strain showed that the phenotype of the mutant was caused b y insertion of the transposon. The wild-type form of devA on a shuttle vector complemented the mutation in M7. Expression of devA by whole f ilaments, monitored following nitrogen stepdown by using luxAB as the reporter, increased ca. eightfold during differentiation; the increase within differentiating cells was much greater. The deduced sequence o f the DevA protein shows strong similarity to the ATP-binding subunit of binding protein-dependent transport systems. The product of devA ma y, therefore, be a component of a periplasmic permease that is require d for the transition from a proheterocyst to a mature, nitrogen-fixing heterocyst.