A polynucleotide sequence is provided, comprising: a nucleic acid sequence having at least 75% identity to SEQ ID NO: 1, wherein said nucleic acid sequence encodes recombinant Bacillus anthracis Protective Antigen (rPA); or a fragment of said nucleic acid sequence wherein said fragment encodes a fragment of recombinant Bacillus anthracis Protective Antigen (rPA).Also provided are expression vectors and host cells comprising the polynucleotide sequence of the invention, and methods for producing rPA or a fragment thereof.The invention further provides antigenic compositions and corresponding methods and uses for inducing an immune response.