Complete genomic sequence of the filamentous nitrogen-fixing Cyanobacterium anabaena sp strain PCC 7120

The nucleotide sequence of the entire genome of a filamentous cyanobacteriu m, Anabaena sp. strain PCC 7120, was determined. The genome of Anabaena con sisted of a single chromosome (6,413,771 bp) and six plasmids, designated p CC7120 alpha (408,101 bp), pCC7120 beta (186,614 bp), pCC7120 gamma (101,96 5 bp), pCC7120 delta (55,414 bp), pCC7120 epsilon (40,340 bp), and pCC7120 zeta (5,584 bp). The chromosome bears 5368 potential protein-encoding genes , four sets of rRNA genes, 48 tRNA genes representing 42 tRNA species, and 4 genes for small structural RNAs. The predicted products of 45% of the pot ential protein-encoding genes showed sequence similarity to known and predi cted proteins of known function, and 27% to translated products of hypothet ical genes. The remaining 28% lacked significant similarity to genes for kn own and predicted proteins in the public DNA databases. More than 60 genes involved in various processes of heterocyst formation and nitrogen fixation were assigned to the chromosome based on their similarity to the reported genes. One hundred and ninety-five genes coding for components of two-compo nent signal transduction systems, nearly 2.5 times as many as those in Syne chocystis sp. PCC 6803, were identified on the chromosome. Only 37% of the Anabaena genes showed significant sequence similarity to those of Synechocy stis, indicating a high degree of divergence of the gene information betwee n the two cyanobacterial strains.