At 28 degrees C, synthesis of protein cyst coat in ciliates of Colpoda steinii is induced by washing with water and, as judged by glutamic acid assays and incorporation studies with l-[U-(14)C]leucine, starts about 30min after the cells have stopped swimming and is largely complete 90min later. During this time up to 70% of the protein synthesized by the cell is coat protein. 2. When cells were placed in l-[U-(14)C]leucine at low concentrations (0.25-0.76mm) during the period of coat synthesis there was no lag in uptake. Only a small proportion of the leucine incorporated into the coat was from the external substrate, implying that the rate of radioactive isotope incorporation measured the rate of transport of amino acid into the cell. Transport of l-[U-(14)C]leucine into the cell was markedly stimulated by l-glutamic acid and l-lysine. 3. When cells were placed in l-[U-(14)C]leucine at high concentrations (38mm) the rate of incorporation was considered to measure the rate of protein synthesis, but because the latter may have been affected by substrate it is concluded that such measurements are of doubtful value.
