Arginine methylation of NAB1 acts as a master control switch for LHCII translation in Chlamydomonas reinhardtii
Olga Blifernez, Lutz Wobbe, and Olaf Kruse
Department of Biology/ Algae Biotechnology & Bioenergy, CeBiTec, Bielefeld, Germany
Photosynthetic organisms have developed many short- and long-term light adaptation strategies. One important long-term acclimatization mechanism involves the regulation of the expression of the nuclear-encoded light harvesting complex (LHCBM) genes. We were able to identify the RNA-binding protein NAB1 (nucleic acid binding protein 1) which acts as a translational repressor for LHCII proteins in C. reinhardtii. In vitro and in vivo RNA-binding as well as polysome analyses confirmed that NAB1 selectively binds to certain LHCBM isoform mRNAs in a subpolysomal high molecular weight RNA-protein complex. Binding of NAB1 represses LHCBM-mRNA translation via sequestration in translationally silent mRNPs (messenger ribonucleoprotein complexes). Recent research data regarding post-translational modifications of NAB1 indicate that the specific repressor activity of NAB1 is regulated by methylation of arginines in its GAR (glycine-arginine rich) domain. Arginine methylation could be demonstrated in vitro and in vivo by mass spectrometry studies of NAB1 purified from C. reinhardtii. Inhibitor studies revealed that arginine methylation is vital for the repressor function of NAB1.
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