Infectious cDNA clones of porcine reproductive and respiratory syndrome virus and expression vectors thereof

A method of producing a full-length infectious North American PRRSV cDNA having a sequence at least 98% identical to SEQ ID NO:1, the method comprising the steps of:

• (a) purifying viral genomic RNA from a North American PRRSV virus;
• (b) generating five overlapping cDNA fragments from the viral genomic RNA using primer pairs comprising:
• i. SEQ ID NO:2 and SEQ ID NO:6;
• ii. SEQ ID NO:5 and SEQ ID NO:8;
• iii. SEQ ID NO:7 and SEQ ID NO:10;
• iv. SEQ ID NO:9 and SEQ ID NO:13;
• and
• v. SEQ ID NO:11 and SEQ ID NO:4;
• (c) preparing five primary clones, each primary clone comprising a cDNA fragment generated in step (b);
• (d) preparing intermediate clones, each intermediate clone comprising at least two contiguous primary clones from step (c);
• and
• (e) combining the intermediate clones of step (d) in a cloning vector to obtain a full-length cDNA clone;
• and
• (f) operably linking at least one promoter sequence to the transcriptional start site of the full-length cDNA clone to obtain a full-length infectious North American PRRSV cDNA having a sequence at least 98% identical to SEQ ID NO:1.