The N TAILD3 gene construct, encoding residues 401-516 of the MV N protein with an N-terminal hexahistidine tag plus a C-terminal Flag sequence, was obtained using the plasmid pet21a/N as template. Forward primer (5 0 -gatagaaccatgCA TCATCATCATCATCATactactgaggacaagatcagtaga-3 0 ) was designed to introduce a hexahistidine tag encoding sequence (upper case) at the N terminus of N TAIL , and reverse primer (5 0 -gtcttaTTTGTCGTCATCGTCTTTATAATCtataggggtgtcc gtgtctgagcc-3 0 ) was designed to introduce a Flag encoding sequence. The PCR amplification product was further used as template in a second PCR step, using forward primer (5 0 -ggggacaagtttgtacaaaaaagcaggcttcgaaggagatagaaccatgCATCA TCATCAT-3 0 ) and reverse primer (5 0 -ggggaccactttgtacaa gaaagctgggtcttaTTTGTCGTCATCGTCTTT-3 0 ), which were designed to introduce an AttB1 and an AttB2 site (bold), respectively. After purification, the PCR product was cloned into the pDest14 vector to yield pDest14/N TAILD3 .