Infectious cDNA of north american porcine reproductive and respiratory syndrome (PRRS) virus and uses thereof

An isolated DNA molecule comprising a DNA sequence encoding an infectious RNA molecule encoding a Porcine Reproductive and Respiratory Syndrome (PRRS) virus, wherein said encoding DNA sequence is selected from the group consisting of:

• (a) SEQ ID NO:1;
• (b) a sequence that has at least 70% identity to SEQ ID NO:1;
• and
• (c) a sequence that hybridizes to the complement of SEQ ID NO:1 under highly stringent conditions which comprise hybridization to filter bound DNA in 0.5M NaHPO4, 7% SDS, 1 mM EDTA at 65° C., and washing in 0.1×SSC/0.1% SDS at 68° C.;
• and
• wherein, in all cases, said isolated DNA molecule (1) lacks an encoding DNA sequence corresponding to all of amino acids 616 through 752 (SEQ ID NO:
• 1 positions 3186-3596) or all of amino acids 628 through 759 (SEQ ID NO:
• 1 positions 3222-3617) in the hypervariable region of the nonstructural protein 2-coding region of PRRS ORF1a;
• (2) wherein said isolated DNA molecule does not comprises a nucleotide sequence, within said PRRS encoding sequence, that encodes a detectable heterologous antigenic epitope;
• and (3) wherein the DNA sequence than encodes the infectious RNA molecule is operably linked to a promoter.