Precursor Molecules of Transfer Ribonucleic Acids in Escherichia coli

The accumulation and a method of isolation of a population of precursor tRNAs from Escherichia coli χ402 treated with chloramphenicol or starved for methionine are described. Two groups of precursor tRNAs, designated α and β, were separated by gel filtration. They differ significantly in size and structure. Although both species, when treated with crude maturation enzymes, yield tRNAs, the longer precursors (α, about 200 nucleotides long), which are apparently less stable, are transformed into RNAs with the same size as β (about 120 nucleotides) and tRNAs. That these two groups of RNAs are indeed precursor tRNAs is proven by the facts that the precursor tRNA peaks, isolated by reversed phase chromatography, disappeared with time and showed sequence homology to tRNAs by competitive hybridization. Whether the longer species (α) are the direct primary transcripts of DNA and contain more than one tRNA sequence is not certain at present.