In vitro translation of elastin mRNA and processing of the translated products and the signal sequence of elastin a

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Abstract
Chick embryo aorta mRNA were translated in a gel-filtered reticulocyte lysate. The translated products showed 2 elastin-related proteins (a and b; relative mass .apprx. 70,000). The translated elastin a protein was separated essentially free of the b protein by centrifugation and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. The a protein was then electroeluted from the SDS-polyacrylamide gel and a partial sequence was determined by automated Edman degradation. The NH2-terminal presequence of the elastin a protein was determined. The assigned sequence is identical to that reported for the b protein. Translation of chick embryo aorta mRNA in the presence of dog pancreas microsomal membranes segregated the a and b proteins into membrane vesicles and cotranslationally cleaved their respective presequences. The processed a and b elastin proteins were isolated together and NH2-terminal proline positions were determined. These proline positions 4 and 8 are identical to those for NH2-terminal sequence for tropoelastin. The signal peptidase apparently removes the 24-residue signal peptide and thus directly generates the tropoelastin sequence, with no NH2-terminal prosequence as the intermediate.