By definition, temperature-sensitive (ts) Sec mutants accumulate a full-length GFP-fusion secretory protein at an intermediate location in the secretory pathway when cells are incubated at the non-permissive temperature. The entire GFP-fusion protein must be synthesized in order for you to visualize it. Any mutation that prevents synthesis of the entire protein will not be detected in a Sec mutant screen because there is nothing to see. With this in mind, which of the following three P54SRP ts mutants would generate a Class A Sec phenotype at the non-permissive temperature? A. ts P54SRP does not bind to the N-terminal signal sequence at the non-permissive temperature.
B. ts P54SRP cannot hydrolyze GTP at the non-permissive temperature.
C. ts P54SRP cannot bind to the SRP receptor α subunit at the non-permissive temperature.
D. Both (a) and (b) would generate a Sec A phenotype.
E. Both (a) and (c) would generate a Sec A phenotype.
F. Both (b) and (c) would generate a Sec A phenotype.