The primary structure of maize and tobacco 5 S rRNA

Mature miRNAs form secondary structure, which suggests their function beyond RISC

The generally accepted model of the miRNA-guided RNA down-regulation suggests that mature miRNA targets mRNA in a nucleotide sequence-specific manner. However, we have shown that the nucleotide sequence of miRNA is not the only determinant of miRNA specificity. Using specific nucleases, T1, V1 and S1 as well as NMR, UV/Vis and CD spectroscopies, we found that miR-21, miR-93 and miR-296 can adopt hairpin and/or homoduplex structures. The secondary structure of those miRNAs in solution is a function of RNA concentration and ionic conditions. Additionally, we have shown that a formation of miRNA hairpin is facilitated by cellular environment.Looking for functional consequences of this observation, we have perceived that structure of these miRNAs resemble RNA aptamers, short oligonucleotides forming a stable 3D structures with a high affinity and specificity for their targets. We compared structures of anti-tenascin C (anti-Tn-C) aptamers, which inhibit brain tumor glioblastoma multiforme (GBM, WHO IV) and selected miRNA. A strong overexpression of miR-21, miR-93 as well Tn-C in GBM may imply some connections between them. The structural similarity of these miRNA hairpins and anti-Tn-C aptamers indicates that miRNAs may function also beyond RISC and are even more sophisticated regulators, that it was previously expected. We think that the knowledge of the miRNA structure may give a new insight into miRNA-dependent gene regulation mechanism and be a step forward in the understanding their function and involvement in cancerogenesis. This may improve design process of anti-miRNA therapeutics.

Canine 5S rRNA: nucleotide sequence and chromosomal assignment of its gene cluster in four canid species

The purpose of this study was to determine the nucleotide sequence of canine 5S rRNA and use this information to develop a molecular probe to assign the gene locus to chromosomes of the dog and three other related canid species using fluorescence in situ hybridization. The nucleotide sequence of canine liver 5S rRNA is 120 base pairs long and identical to the 5S rRNA nucleotide sequence of all other mammalian species investigated so far. A single 5S rRNA gene cluster was localized pericentromerically on chromosomes of four canid species: dog 4q1.3, red fox 4q1.3, blue fox 3q1.3 and Chinese raccoon dog 8q1.3. Chromosome arms carrying the 5S rRNA gene cluster showed striking similarities in their QFQ banding patterns, suggesting high conservation of these chromosome arms among the four species studied. The chromosomal assignments of 5S rRNA genes are among the first gene mapping results for the blue fox and the Chinese raccoon dog, and are in accordance with published data on comparative chromosome maps from human, dog, red fox, blue fox and raccoon dogs.

Purification and characterization of transcription factor IIIA from higher plants

Transcription factor IIIA (TF IIIA) binds and specifically activates transcription of eukaryotic 5S rRNA genes. It also forms a 7S ribonucleoprotein complex with mature 5S rRNA. Here, we describe the purification and properties of pTF IIIA from higher plants. The purified protein from tulip (Tulipa whittalii) has a molecular mass of about 40 kDa and also binds 5S rRNA and 5S rRNA genes. pTF IIIA also facilitates the transcription of a 5S rRNA gene in a HeLa cell extract.

The nucleotide sequence of 5S ribosomal RNA from the parasitic nematode Ascaris suum. Evolutionary relationships in nematodes

We have determined the nucleotide sequence of 5S ribosomal RNA from the parasitic nematode Ascaris suum. The analysis of all Nematoda 5S rRNAs and their genes shows that this group must have diverged from other Metazoa at early stages of evolution. This conclusion is supported by the sequence variability in single-stranded regions which are strongly conserved in animal 5S rRNAs.

The nucleotide sequence of ribosomal 5s RNA from sorrel

The nucleotide sequence of ribosomal 5S RNA from sorrel (Rumex acetosa) was determined. This sequence shows the highest homology to Chenopodiaceae and Cruciferae ribosomal 5S RNA when compared to other dicotyledones' 5S rRNA.

The primary structure of Harpalus rufipes 5S ribosomal RNA: a contribution for understanding insect evolution

The nucleotide sequence of 5S ribosomal RNA from the beetle Harpalus rufipes was determined and compared with primary structures of other insect 5S rRNAs. Sequence differences between two beetle 5S rRNAs may represent phylogenetic markers specific for two groups of Coleoptera - Adephaga and Polyphaga. Analysis of all insect sequences using parsimony allowed us to infer a phylogenetic tree of insects, which is consistent with morphological and paleobiological data.

The dynamic conformation of plant cytoplasmic 5S rRNAs

Recently we have proposed a new three-dimensional model of plant 5S rRNAs structure. To verify this proposal we present here new data on RNase T1 digestion and hydroxyl radical hydrolysis of lupin and wheat germ 5S rRNAs at various buffer and temperature conditions. Interestingly, the guanosine residues 85-87 in the loop D of these RNAs, are resistant to RNase T1 at native but not at denaturating conditions. On the other hand, the reaction of 5S rRNA with the hydroxyl radicals showed different reactivity of many nucleotides in various parts of the molecule and suggest conformational changes, which occur mostly in the loops. The experimental data clearly support involvement of the nucleotides occupying conserved positions in the loops in the tertiary interactions in plant 5S rRNA structure.

A-Z-RNA conformational changes effected by high pressure

This paper reports evidence obtained by circular dichroism (CD) spectroscopy measurements indicating that two oligoribonucleotide duplexes with the alternating purine-pyrimidine sequences r(GC)6 or r(AU)6 change their A-RNA conformation under high pressure. Under the high-pressure conditions at which B-Z-DNA transition easily occurs, RNA acquires a conformation which only differs slightly from that of A-RNA. However, exposure of r(GC)6 or r(AU)6 to high pressure (6 kbar) in the presence of 5 M NaCl causes a conformation change of both oligoribonucleotide duplexes from their A- to their Z-RNA form. The departure of RNA or DNA duplexes from their original conformations under high pressure depends on the water structure itself and involves displacing an active (structural) water molecule outside the nucleic acid molecules. Experiments carried out until now in many laboratories have shown that B-Z or A-Z transitions of DNA or RNA, respectively, do not depend on the conditions applied, but the common mechanism for these processes seems to be dehydration. This same effect can be observed either at high salt concentrations or in the presence of an alcohol or at high pressure. Our results also support the view that the higher stability of RNA compared with DNA duplexes is due to the strong interaction of the 2'-hydroxyl groups of RNA with water molecules.

Unfolding of the tertiary structure of specific tRNA and ribosomal 5S RNA from plants as studied with hydroxyl radicals

Ribosomal 5S RNA is present in all eubacterial and eukaryotic ribosomes. Despite a large amount of experimental data on the primary and secondary structures of these types of molecules, details of their tertiary structure and their precise function in protein biosynthesis are still not known. Recently we have proposed a new model for the tertiary structure of plant 5S rRNA. In this study we applied the Fe(II)-mediated cleavage reaction to test the model. The data presented here provide experimental evidence that in the 5S rRNA molecule only a few nucleotides are buried in the tertiary structure. Similar experiments performed with methionine initiator tRNA gave results which imply the difference in its structure when compared with the X-ray structure of yeast tRNAPhe.

Higher plant 5S rRNAs share common secondary and tertiary structure. A new three domains model

A new model of secondary and tertiary structure of higher plant 5S RNA is proposed. It consists of three helical domains: domain alpha includes stem I; domain beta contains stems II and III and loops B and C; domain gamma consists of stems IV and V and loops D and E. Except for, presumably, a canonical RNA-A like domain alpha, the two remaining domains apparently adopt a perturbed RNA-A structure due to irregularities within internal loops B and E and three bulges occurring in the model. Bending of RNA could bring loops B and E and/or C and D closer making tertiary interactions likely. The model differs from that suggested for eukaryotic 5S rRNA, by organization of domain gamma. Our model is based on the results of partial digestion obtained with single- and double-strand RNA specific nucleases. The proposed secondary structure is strongly supported by the observation that crude plant 5S rRNA contains abundant RNA, identified as domain gamma of 5S rRNA. Presumably it is excised from the 5S rRNA molecule by a specific nuclease present in lupin seeds. Experimental results were confirmed by computer-aided secondary structure prediction analysis of all higher plant 5S rRNAs. Differences observed between earlier proposed models and our proposition are discussed.

Structural analysis of plant ribosomal 5S RNAs. Visualisation of novel tertiary interactions by cleavage of lupin and wheat 5SrRNAs with ribonuclease H

A model for the tertiary structure of plant 5S rRNA, previously proposed by our laboratory (Joachimiak, A. et al. (1990) Int. J. Biol. Macromol., in press) was tested by specific cleavage of the plant 5S rRNA in the presence of synthetic oligodeoxynucleotides. The hexanucleotides used in this study were complementary to different portions of loops C, D and E, the nucleotides of which have recently been proposed to be involved in tertiary hydrogen bonds. The results obtained strongly support the interaction of loops C and D by nucleotides C34, C35, C36, A37 and G85, G86, G87, U88, respectively. Digestion pattern of loop E (domain gamma, nucleotides 66-110) suggests a possible different arrangement of this part of the plant 5S rRNA molecule, when compared with other eukaryotes.

New model of tertiary structure of plant 5S rRNA is confirmed by digestions with alpha-sarcin

The cytotoxin alpha-sarcin was employed to test the model of secondary and tertiary structures of plant 5S rRNAs, which we recently proposed [(1990) Int. J. Biol. Macromol. (in press)]. alpha-Sarcin is a novel ribonuclease that hydrolyzes phosphodiester bonds adjacent to purines in nucleic acids. The digestion pattern obtained for lupin and wheat germ 5S rRNAs strongly suggests the existence of tertiary interactions between residues C34, C35, C36, A37 and G85, G86, G87, U88 as previously proposed. The results on the secondary structure of plant 5S rRNA are in line with a previously proposed model.

Molecular evolution of plants as deduced from changes in free energy of 5S ribosomal RNAs

The nucleotide sequence of Pinus silvestyris 5S rRNA was determined using two independent methods and compared with other plant 5S rRNAs. It shows more than 90% sequence homology with gymnosperm 5S RNAs. The free energy (delta G) analysis of 5S rRNAs from gymnosperms, angiosperms and the other higher plants revealed that the free energy of this ribosomal RNA decreases with evolution.

The primary structure of lupin seed 5.8 S ribosomal RNA

The lack of colinearity between nucleotide sequence of the lupin 5.8 S rDNA gene (Rafalski, A.J., Wiewiórowski, M. and Soll, D. (1983) FEBS Lett. 152, 241-246) and 5.8 S rRNA of other plants (Erdmann, V.A. and Wolters, J. (1986) Nucleic Acids Res. 14, r1-r59.) prompted us to clarify this point by sequencing the native lupin 5.8 S rRNA. The sequence analysis was carried out using enzymatic and chemical methods. Lupin seed 5.8 S rRNA contains 164 nucleotides, including four modified ones: two residues of 2'-O-methylguanosine, one pseudouridine and one 2'-O-methyladenosine. The nucleotide sequence homology with the other plant 5.8 S rRNAs is approx. 88-96%.

5S-rRNA genes in rice embryos

The 5S-rRNA from the ungerminated and 48-h-germinated rice embryos differs from the wheat, rye and maize by two nucleotides. The 48-h-germinated embryos contain another species of 5S-rRNA which differs by 3 nucleotides from the ungerminated embryos, thereby showing the expression of two 5S-rRNA genes during germination. The 5S-rRNA genes are present in tandem repeats of a 0.3-kb sequence with some length heterogeneity in the rice genome. The 5S-rRNA gene that was sequenced is identical to that of wheat and maize, except for two nucleotides, C and T, which are interchanged at positions 107 and 117. The insert of continuous 5S-rRNA gene in pBR322 was transcribed in vitro much more efficiently than the discontinuous gene. There was no homology between the 184-bp spacer sequence of 5S-rRNA genes in rice and other systems except the presence of the oligo(T) transcription terminator sequence.