Anticodon loop sequences of transfer RNACGASer and transfer RNAIGASer from the posterior silkgland of Bombyxmori L

The adaptive level of tRNAs to their use for synthesizing silk proteins involves three isoaccepting serine tRNAs. The two lipophilic tRNA_2a and tRNA_2b species from the posterior silkgland of the silkworm $\text{Bombyx}\text{mori}$, which are able to decode the UCG and UCU, UCC, UCA respectively, have been purified by counter-current distribution. They have been subjected to pancreatic and T₁ ribonucleases digestion. Resulting oligoribonucleotides have been analyzed and partially sequenced. The IGA anticodon found in the dodecanucleotide: $\text{Y-A-G-A-m}{}^3\text{C-U-}\text{I-G-A}\text{-i}{}^6\text{A-A-ψp}$ for the preponderant tRNA_2b is consistent with the occurrence of UCA as the main serine codon in fibroin mRNA. A CGA anticodon has been detected in the homologous fragment of a minor isoaccepting tRNA_2a.