Most recombinant product was purified from the soluble fraction of the bacterial lysate (Fig. 6A) . The identity of the recombinant product was confirmed by IP studies using anti-N Cl25, and anti-hexahistindine tag mAbs (data not shown). As already observed in the case of full-length N TAIL and N TAIL deletion proteins, N TAILW518 migrates in SDS-PAGE with an apparent MM higher than expected (Fig. 6A) . The mutated protein, displays the same gel filtration elution profile as the wt form (data not shown), leading to an estimated R S of 27 6 3 Å .