Specificity of in Vitro Import in Spinach Leaf Mitochondria and Chloroplasts

In a plant cell, two organelles provide the cells energy requirement, the chloroplast and the mitochondrion. Both organelles have a limited coding capacity and must import more than 90% of their proteins from nuclear coded precursors in the cytoplasm. Import into mitochondria and chloroplasts have been studied for some time but import into plant mitochondria and the sorting phenomenon in a plant leaf cell is a rather new topic for investigations. There has been reports of mis-sorting (1). Post-translational import is believed to follow a similar theme for both mitochondria and chloroplasts. The ATP synthase is present in both chloroplasts and mitochondria. The chloroplast ATP synthase CF1β-subunit is encoded by the chloroplast while the mitochondrion F1β-subunit is nuclear coded. In photosynthetic tissue, chloroplasts have greater relative surface area and thus the mitochondrial F1 precursor has to be effectively directed to the mitochondrion. We investigated the sorting properties for the β-subunit of the β-ATP synthase by using in vitro transcribed/translated the mitochondrial Nicotiana plumbagnifolia F1β and Neurospora crassa F1β. The sorting phenomenon was investigated on two levels, import and processing ability of both organelles for the F1β-subunit.