If the inserted sequence had been complete except for missing the last 54 nucleotides and thus the stop signal), would a working protein be possible?
Yes, but the carboxy-terminus of the protein would be lengthened until a stop codon was reached by the ribosome. With the beginning 401 amino
acids there, the possibility of the protein motifs required for correct protein folding would be high.
No; an altered DNA sequence would lead to an altered amino acid sequence that would misfold. Lacking the termination codon, the ribosome
would continue translating codons in the wrong reading frame until a stop codon is reached. This could lead to an increase in size for the protein,
and the additional motifs may interfere with proper folding,
Both yes and no are probable. DNA sequencing after the inserted gene would need to be done to see whether any stop signals would be in the
correct reading frame or what possible amino acids would be added to the protein.