By sequence analysis, a gene encoding a homolog of the 17-kDa protein antigen of the Gram-negative pathogen Brucella abortus (Hemmen et al., Clin Diagn Lab Immunol 2: 263, 1995) was identified in the nocardioform actinomycete Rhodococcus sp. NI86/21. Database searching also revealed a partial human cDNA sequence for a putative eukaryotic homolog of this presumptive Brucella-specific protein. These proteins display a low bur significant level of similarity with lumazine synthases involved in bacterial riboflavin biosynthesis. In the upstream region, a Rhodococcus gene for a putative regulatory protein of the AsnC family is located.