Final answer:
Without an ER signal sequence, the protein will be translated into the cytosol instead of being directed to the endoplasmic reticulum. This will likely alter its function or cellular location, but it does not necessarily mean it will be degraded.
Step-by-step explanation:
If we make a mutant without an ER signal sequence, the protein will be translated into the cytosol. This is because the ER signal sequence, usually located at the N-terminal end of the protein and consisting of 10-30 amino acid residues, essentially serves as a 'train ticket', directing the protein to the endoplasmic reticulum (ER) for further processing and targeting to specific destinations in the cell, such as secretion or insertion into the plasma membrane. Without this signal sequence, the protein won't be directed to the ER and will instead remain in the cytosol. This could potentially alter its function or prevent it from going to its correct cellular compartment, but it does not mean that the protein will be ubiquitinated and degraded in the proteosome, as this typically occurs with misfolded proteins or those tagged for degradation for other reasons.