          −  CLONING AND EXPRESSION OF RECOMBINANT POLYPEPTIDE FROM THE ERNS CODING REGION OF THE BOVINE VIRAL DIARRHOEA VIRUS IN   M. EKHTELAT¹, M. R. SEYFIABAD SHAPOURI¹, M. GHORBANPOOR NAJAFABADI¹, M. LOTFI² & P. MAHMOODI KOOHI¹ ¹Department of Pathobiology, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Ahvaz; ²Department of Quality Control, Razi Vaccine and Serum Research Institute, Karaj, Iran  Ekhtelat, M., M. R. Seyfiabad Shapouri, M. Ghorbanpoor Najafabadi, M. Lotfi & P. Mahmoodi Koohi, 2012. Cloning and expression of recombinant polypeptide from the Erns coding region of the bovine viral diarrhoea virus in  .    , , No 4, 236−245. Bovine viral diarrhoea (BVD) is an economically important cattle disease with a worldwide distribution. Detection and elimination of animals persistently infected (PI) with bovine viral diarrhoea virus (BVDV) is essential for the control of BVD and eradication of BVDV. Usually, there are no pathognomonic clinical signs of BVDV infection. Diagnostic investigations therefore rely on laboratoryBbased detection of the virus, or virusBinduced antigens or antibodies. Erns as an immunogenic protein of BVDV is genetically and antigenically conserved among different isolates and therefore, a candidate antigen for developing ELISA for serological studies or identification of PI animals. In this study, a segment of BVDV genome corresponding to the sequence coding for Erns was amplified using RTBPCR and cloned into expression vector pMalc2x, under the control of the  promoter. After sequencing of the gene, the recombinant protein was expressed in   BLB21 and analysed by SDSBPAGE and western blotting. The strong promoter of vector pMalc2x allowed a high level of Erns expression. Based on our results it appears that this plasmid construct may be suitable for the production of Erns recombinant antigen and Erns specific antibodies to develop BVDV laboratory diagnostic assays.  : bovine viral diarrhoea, Erns, pMALc2x, recombinant antigen INTRODUCTION Bovine viral diarrhoea (BVD) is one of the most important diseases of cattle worldwide (Gunn  ., 2005). The BVD virus (BVDV) is capable of producing a broad range of clinical signs, ranging from most often asymptomatic infection to severe acute disease with signs from the enteric, reproductive or respiratory orB gans. Bovine foetuses infected with BVDV between days 30 and 125 of gesB tation can develop immune tolerance against the virus and will be born persisB tently infected (PI) (Hilbe  ., 2007). PI animals are virus positive and antibody negative when they are infected with a sole genotype or subtype of BVDV