<P> Signal peptides are extremely heterogeneous and many prokaryotic and eukaryotic signal peptides are functionally interchangeable even between different species however the efficiency of protein secretion is strongly determined by the signal peptide . </P> <P> In vertebrates, the region of the mRNA that codes for the signal peptide (i.e. the signal sequence coding region, or SSCR) can function as an RNA element with specific activities . SSCRs promote nuclear mRNA export and the proper localization to the surface of the endoplasmic reticulum . In addition SSCRs have specific sequence features: they have low adenine - content, are enriched in certain motifs, and tend to be present in the first exon at a frequency that is higher than expected . </P> <P> Proteins without signal peptides can also be secreted by unconventional mechanisms . E.g. Interleukin, Galectin . The process by which such secretory proteins gain access to the cell exterior is termed unconventional protein secretion (UPS). In plants, even 50% of secreted proteins can be UPS dependent . </P>

Translation of antibody proteins in eukaryotic cells is associated with what organelle