Detection of nucleoside Q precursor in methyl-deficient E.coli tRNA

32P-Labeled tRNAAsn was isolated from methyl-deficient E. coli tRNA. Nucleotide sequence analysis showed that tRNAAsn contains three derivatives of the Q nucleoside, possibly Q precursors, in addition to guanosine in the first position of the anticodon. One of the Q precursors was isolated on a large scale. Its UV spectra were identical with those of normal Q, indicating that 7-deazaguanosine structure having a side chain at position C-7 is complete in the Q precursor. No radioactivity was incorporated into Q or Q precursors from either methyl-14Cmethionine, 1-14Cmethionine or U-14Cmethionine, showing that methionine was not directly involved in the formation of Q.