BIOLOGICAL FUNCTIONS OF MODIFIED NUCLEOTIDES IN tRNA MOLECULES （Ⅲ）——SYNTHESIS AND BIOLOGICAL ACTIVITY OF ANALOGS OF YEAST ALANYL tRNA WITH m1I37 REPLACED BY A, G OR C

A thirty-nine nucleotide fragment （nucleotides 38—76） of yeast alanyl tRNA was prepared by using calf spleen phosphodiesterase to delete CmIfrom the 3′-half molecule of this tRNA under controlled conditions. Analogs of yeast alanyl tRNA with A, G or C instead of mIwere synthesized and their biological activities determined. The results indicated that the aminoacylation activity of these analogs was not affected in the rat liver aminoacyl-tRNA synthetase system, compared with natural yeast alanyl tRNA. However, the incorporation activity （i. e. the activity of transferring alanine into proteins） of these analogs was significantly reduced to 20—30% of that of natural yeast alanyl tRNA in the rabbit reticulocyte lysate cell-free protein synthesizing system.