Gene concentration varies in the macronucleus of Tetrahymena

The ratio of amounts of specific genes to total DNA (gene concentration) in different lines of Tetrahymena and at different conditions has been determined by hybridization with specific gene probes. The concentration of the DNA coding for rRNAs is specific for different strains. It also decreases with growth rate, the extent of reduction being different in various species. The rDNA concentration increases unproportionally when the size mutant D9 grows to double the volume upon transfer to the non permissive temperature. rDNA concentration, therefore, changes specifically with physiological status. Genes on other DNA fragments occur in other proportions than the rDNA. The concentration of the S25 ribosomal protein gene is reduced significantly upon entering the stationary phase, while the concentrations of the other genes tested appear unchanged. The results indicate that the amounts of specific DNA molecules in the macronucleus of Tetrahymena are controlled depending on the strains used and on the conditions.