A Procedure for Comparing Growing and Non-growing Tetrahymena Cultures: Ribonucleotide Pools in Tetrahymena Starved for the Essential Amino Acid Histidine1

ABSTRACT A new starvation procedure permitted the study of early events in a protozoon's growth cycle. Growing cultures of Tetrahymena that differed from non-growing cultures by one variable were produced by adding histidine to cells deprived of that amino acid in an otherwise complete medium. Alterations of the nucleotide pools were examined in +His and in -His cultures in the period preceding RNA synthesis by cells in +His medium. High performance liquid chromatographic analysis provided a balance sheet for the difference in purine compounds in the two cultures. The change in rNTP levels occurred only when the cells were resuspended in a fresh medium and was not a function of cell density. These observations point to the presence of a factor(s) in the old medium that inhibits the energy charge increase in rNTP and in purine accumulation.