The polyamine content of the tRNA of E. coli.

A sensitive method of polyamine estimation has been adapted to the study of the organic cations of small amounts of nucleic acid. A procedure utilizing phenol extraction, alcohol precipitation, and separation on Sephadex G100 has been devised for the isolation of tRNA at low ionic strength. The procedure is applicable to the isolation of tRNA from liter batches of bacterial culture. With these methods we have examined the polyamines of tRNA isolated from polyauxotrophic strains of E. coli incubated under various physiological conditions and have found the following: (1) The tRNA from relaxed bacteria (TAU rel) harvested during exponential growth is heterogeneous with respect to polyamine content. Some portions of the population contain about one mole of spermidine per mole of tRNA. Some putrescine and an unknown amine are also present in low concentration. (2) After exponential TAU rel is incubated with thymine and uracil in the absence of arginine, the tRNA population is far more homogeneous with respect to polyamine content. The various fractions contain two moles of spermidine per mole of tRNA and a small amount of putrescine. (3) After exponential TAU rel is incubated in the absence of both arginine and uracil, the polyamine pattern of the tRNA resembles that isolated from exponential cells. (4) The tRNA from stringent bacterias harvested during exponential growth is heterogeneous with respect to polyamine distribution and some fractions contain relatively high concentrations of the unknown amine.