Two species of glutamine tRNA were isolated from mouse liver and their nucleotide sequences were determined. The minor glutamine tRNA(tRNAGinuG) that possesses UmUG (where Um stands for 2'-O-methyluridine) as the anticodon sequence was found to have suppressor activity for the UAG termination codon of tobacco mosaic virus RNA in a rabbit reticulocyte in vitro translation system. The amount of this suppressor glutamine tRNA in mouse liver was 1-2% ofthe amount of the major glutanmine tRNA(tRNAeG) that has the CUG anticodon sequence, but it was markedly increased in NIH 3T3 cells infected with Moloney murine leukemia virus and in Ehrlich ascites cells. These results support the hypothesis that tRNAIUG actually functions in vivo as a suppressor tRNA that recognizes the UAG termination codon located at the gag-pol gene junction of Moloney murine leukemia virus and results in the synthesis of the virus-encoded protease.We have reported that Tetrahymena, a ciliated protozoan, contains two glutamine tRNAs that have CUA and UmUA (where Um stands for 2'-O-methyluridine) as their anticodons (1, 2). These two glutamine tRNAs, tRNA81A and tRNA G1nUA, were shown to recognize UAG and either UAG or UAA codons, respectively, in a rabbit reticulocyte, cell-free, protein synthesizing system (2). These results, as well as data on the nucleotide sequences of several ciliate structural genes including Tetrahymena genes, strongly suggested that ciliates use UAG and UAA as glutamine codons, but not as termination codons (3-6). This raised the question of whether this kind of deviation from the universality of the genetic code also occurs in other organisms.Pure et al. (7) reported that yeast glutamine tRNA produced in vivo by transfection of multiple copies of the corresponding tRNA genes with a TTG anticodon sequence weakly suppresses the UAA termination codon.In addition, Yoshinaka et al. (8) showed that a viral protease, coded by Moloney murine leukemia virus (MoMuLV), is a read-through product of the UAG termination codon between the gag and pol genes, with glutamine inserted at the site of the termination codon. These data suggest that glutamine suppressor tRNAs might also be present in other organisms that use the normal genetic code, as a sign of some shared ancestral trait, although, in ciliates, the use of UAG and UAA as glutamine codons may have been a strongly pronounced feature throughout their evolution.This hypothesis prompted us to attempt to isolate natural glutamine suppressor tRNA from other higher eukaryotes, especially from mammalian tissue such as mouse liver. We report here the isolation and nucleotide sequence analysis of a glutamine suppressor tRNA that can recognize the UAG termination codon of tobacco mosaic virus (TMV) RNA in an in vitro protein biosynthesis system. We also report that the amount of this natural glutamine suppressor tRNA, which exists as a minor species of glutamine tRNA in normal mouse cells, is markedly increased in Mo-MuLV-infected mouse cells as well as in Ehrlich ascites cells. ...

Keywords: allogeneic recognition/ascidian hemocyte/phenoloxidase/respiratory burst/exocytotic burst/superoxide anion ABSTRACT. Contact reaction is the morphological expression of allogeneic recognition by hemocytes in the ascidian, Halocynthia roretzi', namely they undergo an exocytotic burst upon contact with non-self (allogeneic) hemocytes in vitro. Wehave found that contact reaction is accompanied by a burst of cyanide-insensitive oxygen consumption that, unlike exocytotic events of mammalianphagocytes, is Ca2+-dependentand does not culminate in the production of superoxide anions or H2O2. Instead, the burst is due to the release of phenoloxidase from hemocytes as known for the self-defense systems in insects and crustaceans. The activity of phenoloxidase released from hemocytes corresponds well to the degree of contact reaction observed under the microscope. Therefore, it is possible to quantify the contact reaction simply by measuring the activity of phenoloxidase released from hemocytes into the medium.

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