Abstract
Crystals of yeast tRNAfMet were iodinated by using a modification of Commerford''s procedure. Chromatographic analysis of nuclease digestion products showed that radioactive iodine binds covalently to the 5 position of 3 nucleotide residues: U8, C73, and C74. These 3 I substitutions were assigned to 3 peaks in a difference Fourier synthesis comparing the iodinated derivative with native tRNAfMet. In this way the positions of U8, C73, and C74 were marked in the crystal structure of yeast tRNAfMet, providing guidepoints for the interpretation of a 4.5-.ANG.-electron density map.