[Optimal conditions of aminoacylation of yeast tRNA Asp and tRNA Trp]

Determination of queuosine derivatives by reverse-phase liquid chromatography for the hypomodification study of Q-bearing tRNAs from various mammal liver cells

Three queuosine derivatives (Q-derivatives) have been found at position 34 of four mammalian so-called Q-tRNAs: queuosine (Q) in tRNA(Asn) and tRNA(His), mannosyl-queuosine (manQ) in tRNA(Asp), and galactosyl-queuosine (galQ) in tRNA(Tyr). An analytical procedure based on the combined means of purified tRNA isolation from liver cells and ribonucleoside analysis by reverse-phase high performance liquid chromatography coupled with real-time UV-spectrometry (RPLC-UV) was developed for the quantitative analysis of the three Q-derivatives present in total tRNA from liver tissues and liver cell cultures. Using this analytical procedure, the rates of Q-tRNA modification were studied in total tRNAs from various mammalian hepatic cells. Our results show that the four Q-tRNAs are fully modified in liver tissues from adult mammals, regardless of the mammal species. However, a lack in the Q-modification level was observed in Q-tRNAs from newborn rat liver, as well in Q-tRNAs from normal rat liver cell cultures growing in a low queuine content medium, and from a rat hepatoma cell line. It is noteworthy that in all cases of Q-tRNA hypomodification, our analytical procedure showed that tRNA(Asp) is always the least affected by the hypomodification. The biological significance of this phenomenon is discussed.

Nuclear tRNA aminoacylation and its role in nuclear export of endogenous tRNAs in Saccharomyces cerevisiae

Nuclear tRNA aminoacylation was proposed to provide a proofreading step in Xenopus oocytes, ensuring nuclear export of functional tRNAs [Lund, E. & Dahlberg, J. E. (1998) Science 282, 2082-2085]. Herein, it is documented that tRNA aminoacylation also occurs in yeast nuclei and is important for tRNA export. We propose that tRNA aminoacylation functions in one of at least two parallel paths of tRNA export in yeast. Alteration of one aminoacyl-tRNA synthetase affects export of only cognate tRNA, whereas alterations of two other aminoacyl-tRNA synthetases affect export of both cognate and noncognate tRNAs. Saturation of tRNA export pathway is a possible explanation of this phenomenon.

Use of a dot blot hybridization method for identification of pure tRNA species on different membranes

The characterization of a tRNA in purification procedures usually involves aminoacylation assays but recently, the hybridization by dot blot with specific oligonucleotides as probes has been used for the tRNA identification. We present here an optimization of a dot blot hybridization method for the tRNA detection by comparing the efficiency of eight different nylon membranes. Neutral 0.22 microns porosity membranes (Nytran, Biodine A) give the best detection efficiency when small quantities of material (less than 40 ng of tRNA) are dotted on filter; by contrast, neutral 0.45 microns porosity membranes (such as Hybond N) are the most efficient when larger quantities of tRNA are dotted on the filter. The described technique allows to detect less than 20 pg of a pure tRNA species. Its use in the identification of Saccharomyces cerevisiae initiator tRNA(Met) in counter-current distribution fractions is shown.

The nucleotide sequence of asparagine tRNA from brewer's yeast

The nucleotide sequence of asparagine tRNA from brewer's yeast has been determined using postlabeling methods. The primary structure is as follows: pG-A-C-U-C-C-A-U-G-m2G-C-C-A-A-G-D-D-G-G-D-D-A-A-G-G-C-m2 2G- U-G-C-G-A-C-U-G-U-U -t6A-A-psi-C-G-C-A-A-G-A-D-m5C-G-U-G-A-G-T-psi-C-A-m1A-C-C-C-U-C-A-C-U-G -G-G-G- U -C-G-C-C-A. Its anticodon G-U-U can recognize the two codons for asparagine.

Sequence of tRNA Ile IAU from brewer's yeast

The nucleotide sequence of tRNAIle from brewer's yeast Saccharomyces cerevisiae was determined. Its primary structure is pG-G-U-C-U-C-U-U-m1G-m2G- C-C-C-A-G-D-D-G-G-D-D-A-A-G-G-C-A-C-C-G-U-G-C-U-I-A-U-t6 A-A-C-G-C-G-G-G-GA-D-m5 C-A-G-C-G-G-T-psi-C-G-m1 A-U-C-C-C-G-C-U-A-G-A-G-A-C-C-A-C-C-A. Its anticodon is I-A-U. It should therefore recognize the three isoleucine codons and is for this reason probably the only isoacceptor tRNA for isoleucine in brewer's yeast. It presents a large homology with its counterpart from Torulopsis utilis (87%).

Primary structure of three tRNAs from brewer's yeast: tRNAPro2, tRNAHis1 and tRNAHis2

The primary structures of three brewer's yeast tRNAs: tRNAPro2 and tRNAHis1 and 2 have been determined (Formula:see text) The U* in the anticodon U*-G-G of tRNAPro2 is probably a derivative of U; tRNAPro2 has 80 per cent homology with mammalian tRNAsPro. tRNAHis1 and tRNAHis2 differ by only 5 nucleotides; they have identical anticodons and may therefore recognize both codons for histidine; they have an additional nucleotide at the 5' end. As in all other sequenced tRNAsHis this nucleotide is not paired with the fourth nucleotide from acceptor adenosine. All three sequenced tRNAs have a low degree of homology with their counterparts from yeast mitochondria.

Specific cleavages of pure tRNAs by plumbous ions

After renaturation some pure tRNAs were submitted to the action of lead acetate 1 . 10(-3) M at pH 7.3 and at 37 degrees C in the presence of either 1 M or 0.5 M NaCl. These tRNAs were specifically cleaved by Pb2+. The exact cleavage points were determined by analysing the oligonucleotides obtained from three yeast tRNAs. In 1 M NaCl, tRNA(Phe) is cleaved after the hUp17 and partially cleaved after Cp73. In 0.5 M NaCl, there are cleaveages after hUp16, hUp17 as well as a partial one after pGP1. In 1 M NaCl tRNA(Asp) is not cleaved, whereas in 0.5 M NaCl 50% of the molecules are cleaved in the anticodon region after Up35, 14% after hUp19 and 6% after hUp16. In 1 M NaCl tRNA(Val) is cleaved in the hU loop: 40% after hUp16 and 60% after CP17. The action of lead on five other pure tRNAs was studied on the analytical scale only, by polyacrylamide gel electrophoresis. They could be classified into two familites, one cleaved mainly in the hU loop, the other in the anticodon loop. The minimal concentrations of Pb2+ required for cleavage were determined for several tRNAs, the most sensitive of which, yeast tRNA(Val), being still cleaved with a concentration of 5 . 10(-6) M in 0.15 M NaCl. Although the cleavage often occurs after hUp, poly (hU) is less sensitive than poly(U). This and other results indicate that cleavages depend more on the conformation than the sequence of the polynucleotide chain, bends in the tertiary structure being lead-sensitive sites. Finally, the amino acid acceptance activities of cleaved tRNA(Phe) and tRNA(Asp) were determined.