An improved method for the purification of tRNA by chromatography on dihydroxyboryl substituted cellulose

Comparison of rat liver and Walker 256 carcinosarcoma tRNAs

The complete nucleotide sequences of both rat liver and Walker 256 mammary carcinosarcoma tRNAAsn reveal that they are identical except for the nucleotide present in the wobble position of the anticodon loop. The rat liver tRNAAsn contains the Q nucleoside, whereas the tumour tRNAAsn contains an unmodified guanosine. The tRNAs from both tissues also show significant quantitative differences in the chromatographic mobilities for isoaccepting species of tRNAAsp, tRNAAsn, tRNAHis and tRNATyr. In addition, chromatographic shifts upon cyanogen bromide treatment and analyses of the alkaline hydrolysates of these tRNAs demonstrate that those of tumour origin contain significantly less Q and Q nucleoside than their normal rat liver counterparts.

The 5' terminal capping of heterogeneous nuclear RNA at different embryonic stages of the sea urchin

5' Terminal cap structures of hnRNA have been characterized and the extent of capping determined as a function of embryonic development. Sea urchin embryo hnRNA contains only the type-1 cap, m7GpppNmpNp, with the type-2 cap, which has a 2'-0-methylated subpenultimate nucleotide, being associated only with stable small nuclear RNAs. These cap 2-containing RNAs are synthesized at a rate of approximately 70 molecules min-1 nucleus-1 compared to approximately 1000 molecules for hnRNA cap 1. Approximately 70% of nuclear cap 1 is associated with greater than 15S RNA in denaturing solvent, but under non-denaturing conditions the percentage is much higher. Cap 1 in low and high molecular weight nuclear RNA have the same kinetics of methyl labeling. Thus all cap 1 structures may belong to a single class either covalent or H-bonded to high molecular weight RNA. hnRNA greater than 15S is 35% capped; however, adding caps in less than 15S RNA gives an estimate of 50% capping for total hnRNA. In development from early blastula to late gastrula, there is little if any change in the extent of capping of hnRNA. These results coupled with others indicate that the fraction of hnRNA molecules serving as precursor to mRNA does not change quantitatively during embryonic development.

A method for purification of peptides from hydrolysates of proteins modified by chemically active analogues of substrates containing cis-diol groups

A simple and rapid column procedure is described for the isolation from protein hydrolysates of peptides containing covalently bound substrate analogues with cis-diol groups. The method is based on complex formation between the cis-diol groups of peptide-bound compounds and dihydroxyborylic groups of a dihydroxyborylaminoethyl cellulose column. The method is useful for isolation of peptide(s) located in or near the active centre of enzymes after their affinity labelling by chemically active analogues of natural substrates like ribonucleotides, sugars, etc.

The localization of tRNAAsp2 genes from Drosophila melanogaster by "in situ" hybridization

Transfer RNAAsp2delta was isolated from Drosophila melanogaster by affinity chromatography on concanavalin A-Sepharose. The tRNA was iodinated "in vitro" with Na [125I] and hybridized "in situ" to salivary gland chromosomes from Drosophila. Subsequent autoradiography allowed the localization of the genes for tRNAAsp2 to the left arm of the second chromosome in the regions 29 D and E.

Detection of unique tRNA species in tumor tissues by Escherichia coli guanine insertion enzyme

The guanine insertion enzyme from Escherichia coli catalyzes exchange of guanine located at the first position of the anticodon of tRNA with radioactive guanine (N. Okada and S. Nishimura, unpublished data). tRNA isolated from various tumors, including slowly growing Morris hepatoma 7794A, incorporated considerable guanine with E. coli guanine insertion enzyme, whereas tRNA isolated from all normal tissues so far tested, except regenerating rat liver, incorporated scarcely any. In the rat ascites hepatoma AH7974, the guanine was mostly incorporated into minor isoaccepting species of tRNAAsp that contained the guanine residue instead of Q base in the first position of the anticodon. This is a sensitive and easy method for identifying unique tRNA species in tumor tissues.

RNA metabolism, manganese, and RNA polymerases of zinc-sufficient and zinc-deficient Euglena gracilis

The three major RNA classes from zinc-sufficient [(+Zn)] and zinc-deficient [(=Zn)] Euglena gracilis have been separated by affinity chromatography on oligo(dT)- and N-[N'-[m-(dihydroxyboryl)phenyl]succinamoyl]aminoethyl (DBAE)-celluloses. The total RNA content and the ribosomal and transfer RNA fractions are the same in (+Zn) and (=Zn) cells. IN (-Zn) cells, the messenger RNA fraction increases, and its altered base composition reveals additional bases and a 2-fold increase in the (G+C)/(A+U) ratio. Since the intracellular content of manganese increases in (-Zn) cells, we have examined its role in determining these changes in RNA composition. An increase in the Mn2+ content from 1 to 10 mM in assays with RNA polymerases I and II from (+Zn) cells and those with the single RNA polymerase from (-Zn) cells decreases the ratio of UMP to CMP incorporated from 1.7 to 1.0, 2.1 to 0.8 and 3.5 to 0.4, respectively. Thus, Mn2+ concentration can significantly alter the products of the enzymatic action of RNA polymerases from both (+Zn) and (-Zn) E. gracilis cells.

The precursor of mouse beta-globin messenger RNA contains two intervening RNA sequences

We have investigated the locations of the poly(A), the mRNA-specific sequences and the RNA sequences that are eventually cleaved from the 1860 nucleotide precursor of mouse beta-globin mRNA. Biochemical and electron microscopic data demonstrate that there are two intervening RNA moieties in the precursor which separate the beta-globin mRNA sequences into three portions containing 480, 205 and 155 nucleotides. One of the two intervening RNA moieties contains 780 nucleotides. The size of the smaller intervening RNA has not been determined precisely, but it is 125 nucleotides or less. The largest mRNA-specific fragment is derived from the 3' terminus of the precursor, and contains the 3' terminal poly (A) and 330 mRNA-specific transcribed nucleotides. At least one, and probably both, intervening RNAs occur within the coding portion of the mRNA sequences. The larger of the intervening RNAs is located next to the 480 nucleotide mRNA-specific fragment, and the smaller intervening RNA is located between the 205 and 155 nucleotide mRNA-specific fragments. These experiments are consistent with the notion that the intervening sequences in the DNA of mouse beta-globin genes are transcribed into the mRNA precursor and are excised from the RNA by post-transcriptional events.

Post-transcriptional modifications of the anticodon loop region: alterations in isoaccepting species of tRNA's during development in Bacillus subtilis

Structural similarities of tRNA's were compared using three sets of isoaccepting species that had previously been shown to undergo significant changes in chromatographic elution properties as a function of developmental stage in Bacillus subtilis. Comparisons of the structures of the tRNA's were based on the composition of their modified nucleosides, comparisons of oligonucleotide elution profiles from RPC-5 columns, and two-dimensional electrophoretic fingerprint analysis of oligonucleotides. The tRNA's studied were tRNA(Lys) (1) and tRNA(Lys) (3); tRNA(Tyr) (1) and tRNA(Tyr) (2); and tRNA(Trp) (1) and tRNA(Trp) (2). The results suggest that the difference among these pairs of isoaccepting species is a difference in the degree of post-transcriptional modifications of the anticodon loop region. The nucleosides involved were N(6)-(Delta(2)-isopentenyl)adenosine (i(6)A), 2-methylthio-N(6)-(Delta(2)-isopentenyl)adenosine (ms(2)i(6)A), and an unknown nucleoside K, which occurred in a position analogous to N-[9-(beta-d-ribofuranosyl)purin-6-ylcarbamoyl]threonine. The amounts of i(6)A and ms(2)i(6)A, determined using total tRNA from exponential-or stationary-phase cells, suggest that the thiomethylation of i(6)A is a pleiotropic phenomenon affecting several tRNA species. As opposed to the situation in Escherichia coli tRNA, where ms(2)i(6)A constitutes about 90% of the total hydrophobic nucleosides at all growth stages, B. subtilis tRNA's have i(6)A as the predominant hydrophobic nucleoside in exponential growth and ms(2)i(6)A as the predominant nucleoside in stationary phase. Thus, the enzyme system which forms i(6)A and the enzyme system which thiomethylates i(6)A are not coordinated during growth in B. subtilis as they are in E. coli. It is suggested that these changes in anticodon loop modifications in B. subtilis may be related to changes in the translational apparatus which occur during sporulation.

Localization of the 5' terminus of late SV40 mRNA

A cap-containing oligonucleotide has been isolated from a T1 ribonuclease hydrolysate of total Simian Virus 40-specific late RNA and its structure has been determined as 7mG(5')ppp(5') mAmpU(m)pUp(Up,Cp)ApGp. This oligonucleotide constitutes the major 5' terminus of both late mRNA species, 16S and 19S. Assuming that viral mRNA "caps" are derived from a 5'-terminal triphosphate or diphosphate, these results mean that late transcription is (mainly) initiated at nucleotide L 308 (numbering system of Simian Virus 40 DNA, cf. Fiers et al. (1978) Nature, 273, 113-120). The cap is followed by a contiguous leader sequence which is at least 194 nucleotides long.

Chemical modification as a probe of conformational changes in transfer ribonucleic acid on aminoacylation

Treatment of Escherichia coli CA265 phenylalanyl-tRNA with 3M-NaHSO3, pH6.0, at 25 degrees C resulted in modification of four bases and in the deacylation of the charged tRNAphe. The similarity of the rates of base modification and of the deacylation of the phenylalanyl-tRNA permitted the isolation of partially modified phenylalanyl-tRNAphe and partially modified deacylated tRNAphe. The sites and extents of base modification in these fractions were determined and found to be the same as those in uncharged tRNAphe modified under identical conditions. These findings are discussed in relation to previous evidence for and against a conformational change in tRNA on its aminoacylation. The methods described should prove adaptable to study of other aminoacyl-tRNA species.

Presence of 5'-terminal cap structures in virus-specific RNA from feline leukemia virus-infected cells

The F-422 line of feline thymus tumor cells, chronically infected with the Rickard strain of feline leukemia virus (R-FeLV), was labeled with 32P, and the total cytoplasmic RNA was isolated. The RNA was centrifuged through sucrose gradients, and R-FeLV virus-specific RNA (vRNA) was located by hybridization of portions of the gradient fractions to R-FeLV complementary DNA. vRNA classes with average sedimentation coefficients of approximately 36S, 28S, 23S, and 15S were identified. Each class of RNA was recovered by hybridized with mercurated R-FeLV complementary DNA, and the hybrids were chromatographed on columns of sulfhydryl-Sepharose to separate them from unhybridized cellular RNA. Although insufficient amount of 36S and 28S vRNA were obtained for further analysis, the 23S and 15S VRNA classes were analyzed to determine the nature of their 5' termini. Each of these vRNA classes was found to contain stoichiometric amounts of cap structures per unit length of RNA, consistent with the presence of one cap per molecule. The structure of the 23S vRNA cap was found to be m7G5'ppp5'GmpAp, whereas that of the 15S vRNA cap was m7G5'ppp5'GmpGp.

Sequence of the 3'-terminal 21 nucleotides of yeast 17S ribosomal RNA

The sequence of the 3'-terminal 21 nucleotides of 17S ribosomal RNA from the yeast Saccharomyces carlsbergensis has been determined to be (Y)G-m62A-m62A-C-U-C-G-C-G-G-A-A-G-G-A-U-C-A-U-U-AOH. This sequence shows extensive homology with the 3'-terminal sequence of 16S rRNA from Escherichia coli including the presence of the two adjacent N6-,N6-dimethyladenosines observed in the small subunit rRNA of eukaryotes as well as of many prokaryotes.

Two adenovirus mRNAs have a common 5' terminal leader sequence encoded at least 10 kb upstream from their main coding regions

The messenger RNAs encoding two late adenovirus serotype 2 (Ad2) proteins, fiber and 100K, were purified by hybridization to restriction endonuclease fragments of Ad2 DNA followed by electrophoresis on polyacrylamide gels containing 98% formamide. The 5' terminal oligonucleotides generated by RNAase T1 digestion of the messengers were selected by dihydroxyboryl-cellulose chromatography. Both mRNAs gave an identical 5'-undecanucleotide with the general structure 7mG5'ppp5'AmC(m)U(C4,U3)G. This undecanucleotide could be removed by mild RNAase treatment from the mRNA after hybridization to DNA fragments containing the main coding sequence of the messenger. In contrast, a small region defined by Bal I-E (14.7-21) protects this undecanucleotide from RNase. A second region contained within both Hind III-B (17-31.5) and Hpa I-F (25.5-27.9), although unable to protect the undecanucleotide, hybridizes to both fiber and 100K mRNAs and protects a similar sequence of 100-150 nucleotides. These observations suggest that both mRNAs contain a long common sequence, complementary to at least two different sites on the Ad2 genome remote from the start of these two genes. The implications of these findings are discussed, and a general mechanism is presented for the biosynthesis of mRNAs from larger precursor molecules, based on intramolecular ligation.

One predominant 5'-undecanucleotide in adenovirus 2 late messenger RNAs

Oligonucleotides containing the 5' termini of adenovirus 2 mRNA are selectively retained on columns of dihydroxyboryl cellulose. When total late adenovirus 2 mRNA was treated with RNAase T1, a single 5' terminal oligonucleotide was isolated, although in several states of methylation. This oligonucleotide has the general structure m7G5'ppp5' AmCmU(C4,U3)G. Since at least twelve individual species of mRNA must be present late after infection, this finding was unexpected and its significance is discussed.

Chromatographic behavior of several mammalian tRNAs on acylated dihydroxyl-borate cellulose and Aminex A-28

Studies of the chromatographic behavior of mammalian tRNAs, from several sources, on acylated DBAE-cellulose indicate that species of tRNA Asn , tRNA Asp and tRNA His can be retained on this matrix, while species of tRNA Tyr, tRNA Asn and tRNA Asp are not retained. Treatment of total rat liver tRNA with cyanogen bromide and subsequent chromatography on Aminex A-28 columns demonstrated that these tRNA species might contain Q (or Q*) nucleoside. However, comparable studies of the tRNA isolated from Walker 256 rat mammary tumor tissue demonstrated that this tumor tRNA almost totally lacks the hypermodified nucleosides Q and Q*. In addition, we have found that at least the major species of rat liver tRNA Asn contains the Q nucleoside. These studies indicate that chromatography on the acylated DBAE-cellulose matrix, couple with the analytical ion-exchange chromatography of cyanogen bromide treated and untreated amino-acyl-tRNA can be a valuable technique for the determination of alterations in the Q (or Q*) nucleoside content of the tRNAs isolated from normal and tumor tissues.

In vivo aminoacylation of transfer ribonucleic acid in Bacillus subtilis and evidence for differential utilization of lysine-isoaccepting transfer ribonucleic acid species

The presence or absence of certain amino acids has different effects on the ability of Bacillus subtilis to sporulate, and the intracellular pool size of amino acids has been reported to vary during sporulation. The idea that these variations might exert a regulatory effect through aminoacylation of transfer ribonucleic acid (tRNA) was investigated by studying the levels of aminoacylation in vivo in the logarithmic or stationary phase of growth. Both the periodate oxidation method and the amino acid analyzer were used to evaluate in vivo aminoacylation. The results indicated that in general the level of aminoacylation of tRNA's remained constant through stage III of sporulation, although there were detectable variations for specific amino acid groups. Our studies also showed that periodate oxidation damaged certain tRNA's; therefore, the results obtained by such a method should be interpreted with caution. Because the damage can affect certain isoaccepting species specifically, the periodate oxidation method cannot be used to establish which isoaccepting species are acylated in vivo. We also investigated the possibility of preferential use of particular tRNA species by polyribosomes. These results demonstrated a preferential use of lysyl-tRNA's at different growth stages. Control mechanisms operating during the early stages of sporulation, therefore, do not affect the overall level of aminoacylation. However, there is an effect on the levels of aminoacylation of specific amino acids and on which isoaccepting species are utilized by the polyribosome system.

Isolation of mammalian tRNAAsp and tRNATyr by lectin-Sepharose affinity column chromatography

tRNAAsp from rabbit liver, rat liver and rat ascites hepatoma was readily isolated by concanavalin A-Sepharose (Con A-Sepharose) affinity column chromatography. tRNATyr from these sources was extensively purified by Ricinus communis lectin-Sepharose column chromatography. These results, together with the chromatographic behaviour of four tRNAs (tRNATyr, tRNAHis, tRNAAsn and tRNAAsp) on acetylated DBAE-cellulose column chromatography suggested that tRNAAsp contains a Q nucleoside species having a mannose moiety while tRNATyr contains Q nucleoside with galactose. The sugars attached in 4-position of cyclopentene diol in the Q molecule are therefore not present at random in the four tRNAs, but present only in each specific tRNA. This is the first case which shows that plant agglutinin interacts with nucleic Acid as well as polysaccharide and glycoproteins.

Isomeric aminoacyl-tRNAs are both bound by elongation factor Tu

Recent suggestions that elongation factor Tu (EF-Tu) is specific for 2'-O-aminoacyl-tRNA, as compared with the 3'-isomer, prompted us to assay [3H]aminoacyl-tRNAs from Escherichia coli terminating in 2'- or 3'-deoxyadenosine for binding to EF-Tu to determine the possible positional specificity of the factor. Binding of modified aminaocyl-tRNAs to EF-Tu-GTP was measured both as a function of the ability of EF-Tu-GTP to diminish the rate of chemical deacylation of [3H]aminoacyl-tRNAs and by gel filtration of the individual ternary complexes. Fifteen different tRNA isoacceptors were tested by the deacylation procedure, including three (tRNAAsp, tRNACys, and tRNATyr) for which isomeric modified aminoacyl-tRNAs were available. All of the modified aminoacyl-tRNAs were protected fromdeacylation, although generally to a lesser extent than the corresponding unmodified species. Six modified tRNA isoacceptors (including tRNATrp and tRNATyr, for which both modified aminoacyl-tRNAs were accessible by enzymatic aminoacylation) were used in gel filtration experiments to permit direct measurement of the individual aminoacyl-tRNA-EF-Tu-GTP complexes. These experiments were also done in the presence of equimolar amounts of the corresponding unmodified [14C]aminoacyl-tRNAs, and the relative affinities for a limiting amount of EF-Tu-GTP were measured. The results were completely consistent with those obtained by the deacylation procedure and indicated that EF-Tu can bind to both positional isomers of aminoacyl-tRNA with no obvious preference for either.

The nucleotide sequence of asparagine tRNA from Escherichia coli

The nucleotide seuquence of Escherichia coli asparagine tRNA was determined to be pU-C-C-U-C-U-G-s4U-A-G-U-U-C-A-G-D-C-G-G-D-A-G-A-A-C-G-G-C-G-G-A-C-U-Q-U-U-t6A-A-phi-C-C-G-U-A-U-m G-U-C-A-C-U-G-G-T-phi-C-G-A-G-U-C-C-A-G-U-C-A-G-A-G-G-A-G-C-C-AOH. Its D-stem and D-loop have almost the same sequence as Escherichia coli aspartate tRNA.

Translation of satellite tobacco necrosis virus ribonucleic acid by an in vitro system from wheat germ

The RNA of satellite tobacco necrosis virus (STNV) is an effective messenger RNA when translated in an in vitro system from wheat germ. This RNA codes for only STNV coat protein, as indicated (1) by coincidence of the tryptic fingerprints of the translation product and of STNV coat protein, (2) by equivalent size of the translation product and STNV coat protein, and (3) by isolation of an initial peptide of the in vitro product containing the amino acid sequence of the N terminus of STNV coat protein. STNV RNA does not contain a 5'-terminal m7G(5')ppp(5')Np---group and translation of STNV RNA by the wheat germ system does not involve prior formation of 5'-terminal m7G(5')ppp(5') nP---groups on STNV RNA. STNV RNA and 125I-labeled STNV RNA form a specific initiation complex when incubated with initiator tRNA, GTP, initiation factors, and wheat germ ribosomes. Treatment of this specific initiation complex with ribonuclease A allows isolation of an 125I-labeled oligonucleotide protected from ribonuclease A by the initiation complex. This specific oligonucleotide contains approximately 38 nucleotides, including nucleotide sequences that coincide with the codons of the N-terminal amino acids of STNV coat proteins.

Specific replacement of Q base in the anticodon of tRNA by guanine catalyzed by a cell-free extract of rabbit reticulocytes

Guanylation of tRNA by a lysate of rabbit reticulocytes was reported previously by Farkas and Singh. This reaction was investigated further using 18 purified E. coli tRNAs as acceptors. Results showed that only tRNATyr, tRNAHis, tRNAAsn and tRNAAsp which contain the modified nucleoside Q in the anticodon acted as acceptors. Analysis of the nucleotide sequences in the guanylated tRNA showed that guanine specifically replaced Q base in these tRNAs.

Characterization of the 5' termini of hn RNA in mouse L cells: implications for processing and cap formation

An analysis of the phosphorylated and capped 5' termini of the heterogenous nuclear RNA of mouse L cells has revealed four types of structure: pppXp..., ppXp..., pXp..., and m7/GpppXmp.... The 5'triphosphate termini consists exclusively of pppGp... and pppAp..., whereas a large proportion of the 5' monophosphate termini are pUp.... The 5'diphosphate termini contain all four species of nucleotide in relative proportions that are roughly similar to those found at the Xm position of cap structures. These results indicate that initiation of hnRNA transcription occurre exclusively with purine nucleotides, and consequently that the hnRNA molecules containing pyrimidines at the 5' termini very probably arise by cleavages at internal sites of larger primary transcripts. Taken together with previous results relating cap structures of hnRNA and mRNA, the data favor a model in which some mRNA sequences are located at transcriptionally initiated proportions and others in internal regions of their precursors. According to this model, both the mRNA segments derived from initial 5' end, and those derived by cleavage at internal sites could be converted to diphosphate-terminated derivatives, which then condense with GTP to form cap structures according to the mechanism previously described for vaccinia and reovirus mRNA.

Chloroplast DNA codes for transfer RNA

Transfer RNA's were isolated from Euglena gracilis. Chloroplast cistrons for tRNA were quantitated by hybridizing tRNA to ct DNA. Species of tRNA hybridizing to ct DNA were partially purified by hybridization-chromatography. The tRNA's hybridizing to ct DNA and nuclear DNA appear to be different. Total cellular tRNA was hybridized to ct DNA to an equivalent of approximately 25 cistrons. The total cellular tRNA was also separated into 2 fractions by chromatography on dihydroxyboryl substituted amino ethyl cellulose. Fraction I hybridized to both nuclear and ct DNA. Hybridizations to ct DNA indicated approximately 18 cistrons. Fraction II-tRNA hybridized only to ct DNA, saturating at a level of approximately 7 cistrons. The tRNA from isolated chloroplasts hybridized to both chloroplast and nuclear DNA. The level of hybridization to ct DNA indicated approximately 18 cistrons. Fraction II-type tRNA could not be detected in the isolated chloroplasts.

Position of aminoacylation of individual Escherichia coli and yeast tRNAs

Transfer RNAs terminating 2'-or 3'-deoxyadenosine were prepared from unfractionated E. coli and yeast (Saccharomyces cerevisiae) tRNAs and purified to remove unmodified tRNAs. The modified tRNA species were assayed for aminoacylation with each of the 20 amino acids to determine the initial position of tRNA aminoacylation. The E. coli and yeast aminoacyl-tRNA synthetases specific for arginine, isoleucine, leucine, methionine, phenylalanine, and valine, as well as the E. coli glutamyl-tRNA synthetase, aminoacylated only those cognate tRNAs terminating in 3'-deoxyadenosine (i.e., those having a 2'-OH group). On the other hand, those E. coli and yeast synthetases specific for alanine, glycine, histidine, lysine, proline, serine, and threonine, as well as the yeast synthetase specific for glutamine, utilized exclusively those tRNAs having an available 3'-OH group on the 3'-terminal nucleoside, while the E. coli and yeast synthetases specific for asparagine, cysteine, and tyrosine, and the yeast aspartyl-tRNA synthetase, utilized both of the modified cognate tRNAs. The only observed difference in specificity between the E. coli and yeast systems was for tRNATrp, which was aminoacylated on the 2'-position in E. coli and the 3'-position in yeast. The results indicate that the initial position of aminoacylation is not uniform for all tRNAs, although for individual tRNAs the specificity has been conserved during the evolution from a prokaryotic to eukaryotic organism.

A method for the isolation of specific tRNA precursors

tRNA affinity chromatography, based on complex formation between tRNAs with complementary anticodons, has been applied to the isolation of specific tRNA precursors. When [32P]RNA, isolated from an Escherichia coli strain containing a thermolabile ribonuclease P, was chromatographed on resin-bound yeast phenylalanine tRNA, precursor tRNAGlu (possessing the complementary anticodon) was specifically retained. Likewise, precursor tRNAPhe was isolated from a column of resin-bound E. coli glutamate tRNA. Both precursor tRNAs isolated were monomeric and may be processed products of an originally larger RNA precursor. Both tRNA precursors contain additional nucleotides beyond the 5'-end of the mature tRNA and have all modified bases found in mature tRNA. The method can be extended to isolate other tRNA precursors by affinity chromatography with different tRNAs. Since the principle of complementary anticodon interaction is not restricted to any particular organism, specific precursor tRNAs from other sources may also be isolated in this way.