Gene expression can occur at several points along the pathway from
proteins. In one example of gene expression, the protein insulin must be trimmed to a smaller size.
How is this is an example of gene expression?
Until the protein is trimmed, transcription is blocked by a repressor protein.
Until the protein is trimmed, it is not useful to the cell.
Until the protein is trimmed, the ribosomes are not active.
Until the protein is trimmed, the shape of the
blocks transcription.

Until the protein is trimmed, it is not useful to the cell.

Explanation: After a new polypeptide is produced, it most fold into its proper three-dimensional conformation in order to become biologically active. But before or after folding, the newly synthesized polypeptide may undergo one or more enzymatic processing, these processing reactions are called posttranslational modifications. Posttranslational modifications is the final step of protein synthesis in which the new polypeptide chain is processed into its biologically active form. These posttranslational modifications include proteolytic cleavage, removal of one or more amino acids from the amino acid terminus, addition of acetyl, phosphorylation, carboxyl methyl or other groups to certain amino acid residues.

Insulin and many other proteins are synthesized as large inactive precursor proteins that are proteolytically trimmed to produce their smaller active forms.