Modification of ribonucleic acid by vitamin B6. 1. Specific interaction of pyridoxal 5'-phosphate with transfer ribonucleic acid.
Whole tRNA preparation obtained from a human cell line (HT-29) of colon carcinoma and purified specific Escherichia coli tRNA were reacted with pyridoxal 5'-phosphate, reduced by sodium borohydride and digested with RNase A and snake venom phosphodiesterase. Two-dimensional chromatography of the pyridoxal 5'-phosphate treated tRNA digest showed that pyridoxal 5'-phosphate binds specifically to GMP, presumably in the form of a Schiff base with the exocyclic amino group of the purine. The reaction of pyridoxal 5'-phosphate with whole tRNA was competitively inhibited by N-acetoxy-2-acetylaminofluorene. This suggests that binding occurred primarily to the G20 base residue at the unpaired region of the dihydrouridine loop (Fujimura et al., 1972). The modification of tRNA by pyridoxal 5'-phosphate resulted in the inhibition, to varying extent (10-80%), of amino acid acceptance in the aminoacyl-tRNA synthetase reaction. Defects in codon recognition by pyridoxal 5'-phosphate modified amino acid acylated tRNAs in the presence of the corresponding guanine-containing polynucleotide triplets were observed by the ribosomal binding assay.