We have cloned and characterized the gene encoding Microcystis aeruginosa (strain M228) lectin (MAL), The gene contains 1551 nucleotides and an open reading frame for a protein of 517 amino acids with a predicted molecular weight of 55,159 Da, The carboxyterminal region of MAL has three tandemly repeated homologous domains composed of 61 amino acids. These regions show similarity to the corresponding regions of the alpha-amylase of Clostridium beijerinckii (23% identity). The mal gene lies adjacent to an ORF that dislay homology to cytochrome P-450 and polyketide synthase, Southern hybridization showed that the genomic DNA of the strain M228 contained, in addition to MAL gene (mal), at least two other mal like gene.