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It is known that each aminoacyl-tRNA synthetase (aaRS) specifically recognizes its cognate tRNAs to ensure the correct translation of the genetic information. However, we had previously demonstrated that mammalian mitochondrial seryl-tRNA synthetase (mt SerRS) can markedly misacylate mitochondrial (mt) tRNA(Gln). To investigate extensively misacylation reactions in mammalian mitochondrion, we purified overall twenty-two mt tRNAs from bovine liver, and determined their misacylation activities using mt SerRS. In addition to tRNA(Gln), tRNA(Ala) and tRNA(Asn) showed weak but significant serylation activities, which raises the possibility that each mammalian mt aaRS can misacylate several non-cognate mt tRNAs in varying degrees, but translational fidelity might be maintained by kinetic discrimination of tRNAs in the network of aaRSs.

The formation of long shoots and short shoots, growing out from erect one-year-old stems sprouted from six-year-old pruned stumps of mulberry (Morus alba L. cv. Shin-ichinose), has been studied. In contrast to the branches of the unpruned trees showing an acrotonic growth habit, where only several terminal buds elongate, the buds of these stems, including the basal buds, burst simultaneously in the spring. A few upper shoots continued to elongate until autumn, forming long shoots, whilst the other shoots (lateral shoots) formed short shoots, the apices of which abscinded until early June. Excision of the long shoots before abscission of the apices of the short shoots took place resulted in continued growth of the short shoots and formation of long shoots in the upper portion of the pruned stem. The results suggest that the dominance of the upper shoots (long shoots) is maintained by a correlative control system acting between the apices of long shoots and short shoots.