Precursor relationship of phenylalanine transfer ribonucleic acid from Escherichia coli treated with chloramphenicol or starved for iron, methionine, or cysteine

Abstract

When treated with chloramphenicol, Escherichia coli 15T-produces two new species (IV and V) of transfer ribonucleic acid specific for phenylalanine in addition to the major normal species (II) and two minor normal species (I and III), which are seen as distinct components upon fractionation by chromatography on columns of benzoylated diethylaminoethyl-cellulose. Species IV is produced when cells are grown in iron-deficient medium and is, therefore, probably deficient in the 2-methylthio modification of N6-(A2-isopentenyl)adenosine. A new minor species (Va) also appears under those conditions. All of the new components elute earlier than the major normal species. Addition of chloramphenicol to iron-deficient cells leads to the production of species V, and that production is blocked by rifampin, as is the production of species IV. Thus, species IV and V appear to be transcriptional products. Although E. coli 15Tappears to be rel+, starvation for methionine or cysteine leads to the accumulation of species IV (without addition of chloramphenicol); rifampin blocks the accumulation. Species V is still produced on addition of chloramphenicol to starved cultures. Starvation for arginine or tryptophan does not alter the chromatographic profile from the normal case. Treatment with permanganate indicates that species II and IV contain isopentenyladenosine but that species V does not. Species V appears to be deficient in both isopentenyl and methylthio modifications of adenosine and perhaps at least one other modification, because removing the isopentenyl moiety from adenosine does not convert species IV into species V, but converts it into species Va. A precursor relationship among species V, IV, and II is suggested by following the chromatographic profile of phenylalanine transfer ribonucleic acid during recovery of E. coli from treatment with chloramphenicol; the various species increase and decrease in a sequential manner.

Iron mediated methylthiolation of tRNA as a regulator of operon expression inEscherichia coli

“…Escherichia coli tRNAs which contain the hypermodified nucleoside 2-methylthio-N 6-(2-isopentenyl)-adenosine (ms2i6A) show well characterised chromatographic changes under conditions where iron is not freely available to the organism (1)(2)(3)(4). E. coli growing in the presence of the iron-binding proteins transferrin, lactoferrin or ovotransferrin thus contain a population of altered tRNAs (1).…”

Iron-related modification of bacterial transfer RNA

“…Escherichia coli tRNAs which contain the hypermodified nucleoside 2-methylthio-N6-( 2-isopentenyl)adenosine (ms 2i6A) adjacent to the anticodon (1,2) show well characterized chromatographic shifts when the bacteria are grown in iron deficient media (3,4,5). The altered tRNAs from such iron deficient E. coli lack the methylthio moiety of ms2i6A (3).…”

Bacteriostatic effect of human milk and bovine colostrum on Escherichia coli: importance of bicarbonate

“…Tyrosyl-tRNA from E. coli 0111 growing in undialyzed colostrum adjusted to and maintained at pH 7.4 using NaOH was mainly normal (80%), although it did contain a small amount of the abnormal species (20%). DISCUSSION E. coli grown in media containing less than about 10-7 M Fe3+ contain abnormal species of certain tRNA's (9,14,19). E. coli 0111 inhibited by serum, bovine colostrum, and human milk also contain abnormal species of aminoacyl-tRNA's (7; Griffiths and Humphreys, Proc.…”