STUDIES ON DEVELOPMENT-SPECIFIC MAJOR PROTEINS IN SCLEROTIA OF SCLEROTINIA SCLEROTIORUM, SCLEROTINIA TRIFOLIORUM, AND SCLEROTINIA MINOR (PROTEIN BODIES)
A major protein of approximately 36,000 daltons was identified in sclerotia of Sclerotinia sclerotiorum. The protein was not detected in vegetative cells, indicating that it is development-specific. It accumulated rapidly during sclerotia formation, ultimately comprising 38% of the mature sclerotial protein. The protein did not decrease in concentration in sclerotial residue or appear in vegetative cells when sclerotia germinated myceliogenically. In contrast, the concentration of the protein decreased in sclerotia undergoing carpogenic germination and a small amount of the protein was present in the resultant apothecia. The protein was purified and characterized. It exists as three charge isomers, and contains all 20 common amino acids. The major isomer has an isoelectric point of 6.0; the two minor isomers have isoelectric points of 5.8 and 6.2 respectively. Development-specific major proteins were also identified in sclerotia of Sclerotinia trifoliorum and Sclerotinia minor, which comprised 27 and 31% of the total cellular protein, respectively. Comparative analyses performed on the major sclerotial proteins from the three Sclerotinia species indicated that the proteins are similar, but not identical. Poly(A+)RNA was isolated from presclerotial polysomes of S. sclerotiorum and translated in vitro in a rabbit reticulocyte translation system. Approximately 44% of the incorporation of (\u2735)S-methionine into protein translated from this RNA was incorporated into the major sclerotial protein. Electrophoretic analysis of the in vivo and in vitro synthesized major sclerotial protein of S. sclerotiorum on one dimensional denaturing polyacrylamide gels indicated that the protein is not synthesized as a large precursor. The major protein of S. sclerotiorum was localized in membrane-bound protein bodies , i.e., subcellular organelles of the sclerotium, by transmission electron microscopy using a gold-labelled double antibody technique. The protein is transported across the membrane of the protein body via a mechanism other than a cleavable amino-terminal signal sequence
