PROTEIN SYNTHESIS AND THE CONTROL OF PLANT PROCESSES

Bonner , James . (California Inst. Technology, Pasadena.) Protein synthesis and the control of plant processes. Amer. Jour. Bot. 46(1) : 58-62. Illus. 1959.—Microsomal ribonucleoprotein particles which occur in the cytoplasm of plant, animal, and microbial cells alike, possess the function of protein synthesis, and appear to be responsible for the formation of many, perhaps all, of the soluble cytoplasmic proteins. To the process the microsome contributes information, arranging previously acyl-activated amino acid residues in the abundance and sequence characteristic of the specific enzyme being synthesized. The microsome consists of RNA and of protein. The latter appears to be a structural protein, common to microsomes and not directly related to the protein synthesized by the microsome. The amount of information contained in the RNA of a microsomal particle can be calculated to be sufficient for the synthesis of one or at the most a few species of protein molecules. There must therefore be within the cytoplasm of the cell many different species of microsomes, superficially alike, but each different species bearing in RNA code the information required for the assemblage of but one or a few kinds of protein molecules. Microsomes do not, so far as can be judged, possess the power to reproduce. On the contrary microsomal RNA, and possibly microsomal protein also, appear to be synthesized within the nucleus. Transfer of microsomes from nucleus to cytoplasm is therefore implied and is in fact suggested by a variety of indirect experiments. The transfer of nuclear information to the cytoplasm may well be mediated by the microsomes.