title: Identification and sequence of a gene required for a developmentally regulated DNA excision in Anabaena.
abstract: Vegetative cells of the cyanobacterium Anabaena contain an 11 kb DNA element within the coding region of the nifD gene. This element is excised by site-specific recombination between directly repeated 11 bp sequences at each of its ends during differentiation of nitrogen-fixing cells called heterocysts. Site-specific recombination, leading to the same rejoined nifD gene, was observed during propagation in E. coli of a fragment containing the 11 kb element and flanking sequences. An assay for excision of the element in E. coli was developed, based on mini-Mu-lac transposition into the element. Since the 11 kb element lacks an origin of replication, its excision results in loss of lac and conversion of blue colony-forming cells to white on X-gal plates. Insertion and deletion mutagenesis identified a region of the element needed for excision. Mutations in this region could be complemented by a 6 kb fragment containing an open reading frame that runs counter to those of the nif genes, beginning 240 bp from the recombination site.
mesh_terms: D001483:Base Sequence; D002872:Chromosome Deletion; D000458:Cyanobacteria / Q000235:genetics*; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics; D005809:Genes, Regulator; D009154:Mutation; D010957:Plasmids; D011995:Recombination, Genetic
chemical_list: D004251:DNA Transposable Elements