Extremely large and slowly processed precursors to the Euglena light-harvesting chlorophyll a/b binding proteins of photosystem II

Authors

Arnon Rikin, University of Nebraska - Lincoln
Steven D. Schwartzbach, University of Nebraska at Lincoln

Document Type

Article

Date of this Version

1988

Comments

Published in Proc. Natl. Acad. Sci. USA Vol. 85, pp. 5117-5121, July 1988

Abstract

Antibody to the Euglena light-harvesting chlorophyll a/b binding protein of photosystem II (LHCPII) immunoprecipitated 207-, 161-, 122-, and 110-kDa proteins from total Euglena proteins pulse-labeled for 10 min with [₃₅S]sulfate. The 25.6- and 27.2-kDa LHCPII were barely detectable in the immunoprecipitate. During a 40-min chase with unlabeled sulfate, the amount of radioactivity in the high molecular mass proteins decreased, and the amount of radioactivity in the 25.6- and 27.2-kDa LHCPII increased with kinetics consistent with a precursor-product relationship. The half-life of the high molecular mass proteins was ≈20 min. The major proteins immunoprecipitated from a nuclease-treated rabbit reticulocyte cell-free translation system programmed with Euglena whole cell or poly(A)⁺ RNA had molecular masses corresponding to the molecular masses of the proteins immunoprecipitated from the pulse-labeled in vivo translation products. RNAs of 6.6 and 8.3 kilobases were the only Euglena whole cell and poly(A)⁺ RNAs that hybridized to a 0.7-kilobase EcoRl-BamHI fragment of plasmid pAB165, which contains a portion of the coding sequence for Arabidopsis LHCPII. RNAs of this size are more than sufficient to code for proteins of 207 kDa. Taken together, these findings demonstrate that the LHCPIIs of Euglena are initially synthesized as slowly processed precursors with molecular masses of 207, 161, 122, and 110 kDa.