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A Role for Zinc in the Structural Integrity of the Cytoplasmic Ribosomes of Euglena gacilis^1,2

^a Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167

Zinc deficiency in dark-grown Euglena gracilis Klebs, Z strain Pringsheim, results in the disappearance of cytoplasmic ribosomes. In contrast, ribosomes in zinc-sufficient Euglena are conserved, do not undergo turnover, and can be demonstrated at any stage of growth. The zinc content of ribosomes from zinc-deficient Euglena just prior to ribosomal disappearance is 300 to 380 micrograms of zinc per gram rRNA as compared to 650 to 1280 micrograms of zinc per gram rRNA in ribosomes from zinc-sufficient cells. Ribosomal disappearance is believed to involve a generalized disintegration process related to the lower content of zinc in the ribosomes. Reappearance of ribosomes requires the addition of zinc. It is proposed that adequate zinc may be essential for normal tertiary and quaternary structure of the cytoplasmic ribosomes of Euglena.

¹ Work supported in part by Research Grant 1347-C-2 from the American Cancer Society (Massachusetts Division), Inc.

² This is part of a work submitted in partial fulfillment of the requirements for the Ph.D. degree. A preliminary report has been given (25).