Examination, by PCR analysis, of the attempted mutation of the desC1 and desC2 genes in Anabaena sp. PCC 7120. (A) Design for mutation of the desC1 and desC2 by insertion of the spectinomycin-resistance gene. (B) Genotypic analysis of mutants. Each fragment was amplified by PCR with the indicated primer pairs and visualized by agarose gel electrophoresis. Abbreviations: Spe^r, spectinomycin-resistance gene cassette; ∆desC1, Anabaena 7120 cells in which the desC1 gene was attempted to mutate; ∆desC2, Anabaena 7120 cells, in which the desC2 gene was attempted to mutate.