Specific Polysome Immunoadsorption to Purify an Ammonium-Inducible Glutamate Dehydrogenase mRNA from Chlorella sorokiniana and Synthesis of Full Length Double-Stranded cDNA from the Purified mRNA

A specific polysome immunoadsorption procedure, employing soluble rabbit anti-NADP-GDH IgG and sheep anti-rabbit IgG covalently-linked to an insoluble cellulose matrix, was used to immunoselect polysomes translating mRNA for a chloroplastic ammonium-inducible NADP-GDH in fully induced cells of Chlorella sorokiniana. The immunoselected polysomes were dissociated, and the NADP-GDH mRNA was recovered by oligo (dT)cellulose chromatography. The translatable NADP-GDH mRNA was estimated to be 0.07 and 90% of the total polysomal poly(A)(+)RNA before and after immunoselection of the polysomes, respectively. The immunoadsorption procedure resulted in an 83% recovery and 1,291-fold purification of translatable NADP-GDH mRNA. In vitro translation of the immunoselected poly(A)(+)RNA yielded a single radioactive protein (on sodium dodecyl sufate polyacrylamide gels) with a molecular weight of 58,500, i.e. size of the putative precursor-protein of the NADP-GDH subunit in the holoenzyme in fully induced cells. The purified NADP-GDH mRNA was used for synthesis of a high proportion of nearly full-length single-stranded cDNA and double-stranded cDNA molecules.