Biosynthesis of Trypanosoma brucei variant surface glycoprotein. I. Synthesis, size, and processing of an N-terminal signal peptide.

An N-terminal signal peptide has been identified on a precursor of the variant surface glycoprotein (VSG) of Trypanosoma brucei, synthesised both in vitro and in vivo. An ordered cyanogen bromide (CNBr) cleavage map was constructed for both mature VSG and for precursor VSG, and this allowed a size estimate of the signal peptide to be made by comparison of the N-terminal CNBr peptides produced from each. The signal peptide contains 30-40 amino acids. Analysis of the precursor VSGs produced when nascent polypeptide chains on T. brucei polysomes were completed in the absence of reinitiation showed that the signal peptide is removed before translation is complete and that the same translational start signal is utilised in the trypanosome and in the rabbit reticulocyte protein synthesis system.