IgA1-specific proteinases (Igase) are acknowledged as a pivotal pathogenicity factor in meningococcus (Neisseria meningitidis) and in some related bacteria. These enzymes belong to trypsin-like clan of serine proteases. They exhibit high substrate selectivity being able to discriminate between IgA1 and IgA2. On the other hand, these enzymes are able to distinguish the human IgA1 from IgA1 of non-primate species of mammals. In addition to conventional IgA1-processing enzymes, alternative enzymes were recently reported to occur in meningococci. However, the substrate specificity of the conventional Igase, its role in pathogenesis, and ability to complement functionality remains obscure. Within the framework of the present project we studied the structure of the Igase genes and their products in two highly virulent N. meningitidis serogroup A strains M9 and A208. In particular, we succeeded to find both conventional and alternative Igase genes in each genome: nucleotide sequences of these genes were deposited in the NCBI Gene Bank under the access number AY770504, AY558158, AY558159. The DNA sequence of the conventional Igase was almost entirely conserved in the two strains, whereas the recently discovered alternative Igase (formerly known as meningococcal adhesine, type 1) exhibited occurrence of a variable region spanning about 900 bp in the 5'-terminal part of the gene. Conventional genes from both strains were expressed in E. coli rendering inclusion bodies. The recombinant products were used for immunization of rabbits and exhibited reaction with both recombinant and native antigen from the N. meningitidis cultural medium.