Polish Journal of Microbiology 2009, Vol. 58, No 2, 99104 ORIGINAL PAPER Introduction Brucella abortus is a facultative intracellular gram- negative bacterium that infects humans and domestic animals. Brucellosis is an important zoonotic disease that causes abortion in cattle, and undulant fever in humans. Brucellosis is considered a major health problem in most the countries all over the world (Moreno et al., 2002). To control brucellosis in human, it is necessary to control it in animal first. At present, live attenuated B. abortus strain S19 is used to immunize animals; however, the vaccine has the three following major disadvantages. First, S19 can mainly cause abortion when administered to pregnant cattle; second, S19 is pathogenic for human; third, the vaccine induces anti- bodies in vaccinated cattle, a false manifestation that may be mistaken for field infection diagnosis. There- fore, developing a more effective and safer vaccine is necessary to control the disease (Schurig et al., 2002). Protection against B. abortus is considered to be depended on cell mediate immunity. The B. abortus L7/L12 ribosomal protein has been identified as a ma- jor component in cellular immunity response (Ko and Splitter, 2003; Cloeckaert et al., Oliveira and Splitter, 1994; 1996). Lipopolysaccharide (LPS) of Brucella is an important component in humeral immunity to brucellosis (Huang et al., 1999). A noninfectious vaccine to humans but effective in stimulating a broad protective immune response is needed to control brucellosis. To develop this type of Brucella vaccine, several research groups are pur- suing different strategies, including development of subunit vaccines (Oliveira and Splitter, 1996), utili- zation of bacterial vectors (Onate et al., 1999), and overexpression of protective homologous antigen (Vemulapalli et al., 2000). The B. abortus L7/L12 ribosomal protein has been identified as an immunodominant antigen (Oliveira and Splitter, 1994). The recombinant L7/L12 protein Expression of Human Serum Albumin  L7/L12 (Brucella abortus Ribosomal Protein) Fusion Protein in Saccharomyces cerevisiae IRAJ PAKZAD 1 , ABBAS REZAEE 2 , MOHAMMAD EMANEINI 3 , AHMAD ZAVARAN HOSSEINI 2 , BAHMAN TABBARAEE 4 and MOROVAT TAHERIKALANI 1 * 1 Department of Microbiology, School of Medicine, Ilam University of Medical Sciences, Ilam, Iran 2 Department of Bacteriology, Medical Sciences Faculty, Tarbiat Modares University 3 Department of Microbiology, School of Medicine, Tehran University of Medical Sciences 4 Department of Bacterium Vaccine, Pasteur Institute of Iran Received 24 August 2008, revised 3 April 2009, accepted 5 April 2009 Abstract Brucella abortus is a facultative intracellular gram-negative bacterial pathogen that causes abortion in pregnant cattle and undulant fever in humans. The immunogenic B. abortus ribosomal protein L7/L12 is a promising candidate antigen for the development of subunit vaccines against brucellosis. It has already been expressed in several bacteria and has been used as DNA vaccine. In order to construct yeast expressing vector for the tHSA-L7/L12 fusion protein, the l7/l12 ribosomal gene was amplified by PCR. The expression plasmid pYtHSA-L7/L12 was constructed by inserting the L7/L12 gene into the pYHSA5 shuttle vector (containing inulinase signal sequence, HSA gene and Gal10 promoter). The recombinant vector was transformed into S. cerevisiae and was then induced by galactose. The secreted recombinant fusion protein was detected in supernatant by SDS-PAGE and confirmed by western blot analysis using anti-HSA and anti-L7/L12 antibodies. Fusion protein was purified by affinity chromatography and its amount was approximately 500 µg /liter. Key words: Brucella abortus, gene expression in Saccharomyces cerevisiae, human serum albumin, L7/L12 * Corresponding author: M. Taherikalani, Department of Microbiology, School of Medicine, Ilam University of Medical Sciences, Banganjab, I.R. of Iran, Ilam; phone: (+98) 841-223-5747; fax: (+98) 841-222-7136; e-mail: taherikalani@gmail.com