Uptake and Processing of the Precursor to the Small Subunit of Ribulose 1,5-Bisphosphate Carboxylase by Leucoplasts from the Endosperm of Developing Castor Oil Seeds

Intact leucoplasts from the endosperm of developing castor oil seed were isolated by Percoll density gradient centrifugation. The precursor to the small subunit of ribulose 1,5-bisphosphate carboxylase from pea was synthesized in vitro from hybrid-selected mRNA. Leucoplasts imported this precursor by an ATP-requiring mechanism similar to that described in chloroplasts (AR Grossman et al. 1980 Nature 285: 625-628). The small subunit precursor was processed to a molecular weight that was identical with that of the mature pea small subunit. These results show that leucoplasts, though specialized for fatty acid biosynthesis and not photosynthesis, have a mechanism of protein import similar to that of chloroplasts.