Pfu polymerase was from Promega. Primers were purchased from Invitrogen. The anti-hexahistidine tag mAb was purchased from Qiagen. The anti-flag mAb was purchased from Sigma. The anti-N Cl 25 (Giraudon et al. 1988; Buckland et al. 1989 ) mAb was kindly provided by D. Gerlier.