IgA1-specific proteinases (Igase) are known as a pivotal pathogenicity factor in meningococcus (Neisseria meningitides) and in some related bacteria. These enzymes belong to the trypsin-like clan of serine proteases. They exhibit high substrate selectivity, being able to discriminate between IgA1 and IgA2 and to distinguish the human IgA1 from IgA1 of nonprimate mammalian species [8]. According to recent data, in addition to the conventional IgA1-processing enzymes, meningococci contain alternative enzymes. However, the substrate specificity of the alternative Igase, its role in pathogenesis, and the ability to complement the functionality of the conventional Igase remains obscure. In this study, we investigated the structure of the Igase genes and their products in two highly virulent strains M9 and A208 of N. meningitides serogroup A. In particular, we found both conventional and alternative Igase genes in each genome; the nucleotide sequences of these genes were deposited in the NCBI Gene Bank under the accession numbers AY770504, AY558158, and AY558159. The DNA sequence of the conventional Igase was almost entirely conserved in both strains, whereas the recently discovered alternative Igase (formerly known as type 1 meningococcal adhesin) contained a hypervariable region approximately 900 bp long in the 5′-terminal part of the gene. The conventional genes from both strains were expressed in E. coli in the form of inclusion bodies. The recombinant products were used for immunization of rabbits. The antibodies obtained efficiently reacted with both recombinant and native antigens from the N. meningitides culture medium.