The best way to explain the discrepancy between the normal length of prolactin (199 amino acids) and the length of the polypeptide synthesized in the experiment (227 amino acids) is that in the absence of Signal Recognition Particle (SRP) and the Endoplasmic Reticulum membrane,a prolactin precursor molecule is therefore synthesized.
Prolactin also plays a role in the stimulation of the proliferation of oligodendrocyte precursor cells.
Relating to all, The Signal Recognition Particle plays a crucial role in mediating the transport of secretory and membrane protein to the Endoplasmic Reticulum or plasma membrane.
This can occur both in the prokaryotic or eukaryotic cell.