Figure 3.

SRP stimulates translocation in the presence or absence of NAC. pPL86 mRNA or pG64 mRNA was translated in a wheat germ system in the absence or presence of SRP (SRP(co)). NAC-depleted or mock-depleted ribosome-pPL86 complexes were isolated as in Figure 1, and half the aliquots were supplemented with 50 nM SRP (SRP (post)). (A) Aliquots of the ribosome-pPL86 complexes were incubated with PK-RM, and translocation was assayed as in Figure 1B. (B) Aliquots of the ribosome-pPL86 complexes and the ribosome-pG64 complexes were incubated with DSS in the absence of PK-RM to crosslink the signal sequence of the nascent polypeptide to SRP54. The crosslinked product (SRP54*) was resolved from pG64 or pPL86 by PAGE in SDS. The chart in panel A also corresponds to the lanes in panel B.