Nucleic acid and ribosome synthesis by Escherichia coli incubated in 5′,5′,5′-trifluoroleucine

Abstract

If Escherichia coli leucine auxotrophs are transferred to a medium in which leucine is replaced by 5′,5′,5′-trifluoroleucine, DNA, RNA and protein syntheses stop within a short time. During the period of RNA synthesis 50-S and 30-S ribosomes containing trifluoroleucine are formed. In addition, the 37-S and 30-S precursors of the 50-S ribosome accumulate. RNA synthesis in trifluoroleucine is increased: (1) in an RC rel strain; (2) by a nutritional shift-up in the RC rel, but not in the isogenic RC str strain; and (3) by low concentrations of chloramphenicol in the RC str strain. Also, strain W C8 (Leu −, RC str) permits equivalent synthesis of RNA in leucine or trifluoroleucine. In all cases of “improved” RNA synthesis, the ribosome precursors persist. Normal macromolecular and ribosome syntheses, thus, are processes which must be achieved during adaptation of E. coli in a chemostat to growth on trifluoroleucine ( O. M. Rennert and H. S. Anker, Biochemistry, 2 (1963) 471).