STUDIES OF THE ROLE OF THE PROPEPTIDES OF THE ARABIDOPSIS-THALIANA 2SALBUMIN

To investigate the possible roles of the Arabidopsis thaliana 2S album in propeptides with respect to sorting, processing, and stability of t he protein in plant cells, five gene constructions deleting or modifyi ng the propeptides were made based on one of the genes encoding the Ar abidopsis 2S albumin. These constructions were introduced into tobacco (Nicotiana tabacum) plants. Using subcellular fractionation and immun ocytochemistry on ripe seeds, it was demonstrated that none of the pro peptides was necessary for the sorting of the protein. Detailed protei n-chemical analysis of the mature gene products indicated that, for al l of the modified 2S albumin precursors made, the proteins were stably folded and correctly processed. However the latter is less efficient when the internal fragment between the small and the large subunit is missing or when this internal fragment is changed. In an attempt to es tablish a rapid assay system for modified 2S albumin precursors, yeast cells were transformed with the same gene constructs. It was demonstr ated that the processing machinery in yeast cells differs from that in plants, and, in a perhaps related observation, differences in stabili ty of a particular modified protein were observed.