To gain insight into the relaxation process of 89K, His 6-tagged MobA89K, MobC89K and the first 258 aa of MobA89K (designated MobA89KN258) were expressed and purified. When overexpressed at low temperature (16°C), MobA89K and MobC89K were both mainly present in the soluble fractions. Although a majority of the MobA89KN258 protein was present in the inclusion body fractions, sufficient soluble material was produced to recover useful amounts of active protein. The molecular masses of the expressed recombinant proteins agreed well with those predicted. All proteins were purified to > 95% homogeneity after metal ion chelating chromatography and gel filtration (Fig. S1 ).