A photoactivatable synthetic transit peptide labels 30 kDa and 52 kDa polypeptides of the chloroplast inner envelope membrane

A 24‐residue transit peptide based on the sequence of a precursor of the small subunit of wheat ribulose‐1,5‐bisphosphate carboxylase (Rubisco) was synthesized. The transit peptide was converted into a radioactive azido derivatised analogue. Photoactivation of the radiolabelled transit peptide analogue with isolated inner and outer membranes of the chloroplast envelope intensely labelled two proteins of 30 kDa and 52 kDa. In the outer membrane only the 52 kDa polypeptide was labelled. These findings are consistent with a recent report on the identification of the 30 kDa receptor protein for protein import in the chloroplast envelope contact zones [(1988) Nature 331, 232–237].