POLYSOMES OF THE SEA URCHIN EMBRYO: NATURE OF SO-CALLED "CYCLIC AMINO ACID INCORPORATION" AND CONDITIONS TO PREPARE CELL-FREE SYSTEMS FOR PROTEIN SYNTHESIS

Cyclic formation of active polysomes in a cell-free system, as reported previously, could not be demonstrated under the conditions reported. However, cyclic fluctuation was observed in incorporation of amino acids into the hot TCA-insoluble fraction. Failure to demonstrate polysome formation seemed to be due to the lack of GTP and to the necessity to protect SH groups during preparation of the system and its assay. Addition of exogenous GTP and ME effectively restored polysomal activity in the cell-free system. The previously reported cyclic incorporation of amino acids into the hot TCA-insoluble fraction in cell-free systems in the absence of these reagents might be due to cyclic variation in some partial reactions or some phenomenon other than protein synthesis.