Figure 3.

Effect of urea and incubation times on the stability of the SRP68/72 interaction. (A) Stability of 68e′/H72b′. Complexes were coexpressed in E. coli and subjected to increasing urea concentrations and incubation times. Polypeptides, either free or associated with Ni-NTA magnetic agarose beads, were visualized by SDS PAGE as described in “Materials and Methods” section. Dashed lines indicate the urea concentration that led to the formation of equal amounts of complex and free 68e′. The insert shows the stability of the complex over time when incubated in 1 M urea. (B) SRP68/72H was coexpressed in S. cerevisiae and purified as described in “Materials and Methods” section. Dashed lines indicate the urea concentration (∼5 M) that led to the formation of equal amounts of complexed and free polypeptides. The insert shows the stability of the 68/72H heterodimer over time when incubated in 5 M urea. (C) Depiction of the interacting components in the assay.