The N TAILHNFC gene construct, encoding residues 401-525 of the MV N protein with an N-terminal hexahistidine tag and a C-terminal Flag sequence (dykddddk) (Brizzard et al. 1994) , was obtained using the plasmid pDest14/N TAILHN as template. Forward primer (5 0 -ggggacaagtttgtacaaaaaagcaggcttcgaaggagata gaaccatgCATCATCATCAT-3 0 ) was designed to introduce an AttB1 site (bold), and reverse primer (5 0 -gtcttaTTTGTCGTCAT CGTCTTTATAATCgtctagaagatttctgtcattgta-3 0 ) was designed to introduce a Flag encoding sequence (upper case). The PCR amplification product was further used as template in a second PCR step, using the same forward primer as above, and reverse primer (5 0 -ggggaccactttgtacaagaaagctgggtcttaTTTGTCGTCAT CGTCTTT-3 0 ), which was designed to introduce an AttB2 site (bold). After purification, the PCR product was cloned into the pDest14 vector to yield pDest14/N TAILHNFC .