Studies on polynucleotides, XLIX. Stimulation of the binding of aminoacyl-sRNA's to ribosomes by ribotrinucleotides and a survey of codon assignments for 20 amino acids.

coverslip. When KB cells were grown on these composite coverslips and treated with directin, the orientation of the cells followed the longitudinal direction of the coverslip in a zigzag fasion. Experiments with different kinds of glass and other substrates are now in progress. Summary.-We have found an agent in extracts derived from human urine which can be identified by its induction of directional growth of malignant cells in a defined in vitro system. The extract sensitizes malignant cells to submicroscopic, directional clues in their environment. Nine cell lines have been examined so far, four malignant and five normal ones. The normal cell lines studied did not respond to directin.