Splicing of eukaryal intron-containing tRNAs requires the action of the heterotetrameric splicing endonuclease, which is composed of two catalytic subunits, Sen34 and Sen2, and two structural subunits, Sen15 and Sen54. Here we report the solution structure of the human tRNA splicing endonuclease subunit HsSen15. To facilitate the structure determination, we removed the disordered 35 N-terminal and 14 C-terminal residues of the full-length protein to produce HsSen15(36-157). The structure of HsSen15(36-157), the first for a subunit of a eukaryal splicing endonuclease, revealed that the protein possesses a novel homodimeric fold. Each monomer consists of three alpha-helices and a mixed antiparallel/parallel beta-sheet, arranged in a topology similar to that of the C-terminal domain of Methanocaldococcus jannaschii endonuclease. The dimeric interface is dominated by a beta-barrel structure, formed by face-to-face packing of two, three-stranded beta-sheets. Each of the beta-sheets results from reciprocal parallel pairing of one beta-strand from one subunit with two other beta-strands from the symmetric subunit. The structural model provides insights into the functional assembly of the human tRNA splicing endonuclease. 相似文献
Using a comparative genomics approach we demonstrate a negative correlation between the number of codon reassignments undergone
by 222 mitochondrial genomes and the mitochondrial genome size, the number of mitochondrial ORFs, and the sizes of the large
and small subunit mitochondrial rRNAs. In addition, we show that the TGA-to-tryptophan codon reassignment, which has occurred
11 times in mitochondrial genomes, is found in mitochondrial genomes smaller than those which have not undergone the reassignment.
We therefore propose that mitochondrial codon reassignments occur in a wide range of phyla, particularly in Metazoa, due to
a reduced “proteomic constraint” on the mitochondrial genetic code, compared to the nuclear genetic code. The reduced proteomic
constraint reflects the small size of the mitochondrial-encoded proteome and allows codon reassignments to occur with less
likelihood of lethality. In addition, we demonstrate a striking link between nonsense codon reassignments and the decoding
properties of naturally occurring nonsense suppressor tRNAs. This suggests that natural preexisting nonsense suppression facilitated
nonsense codon reassignments and constitutes a novel mechanism of genetic code change. These findings explain for the first
time the identity of the stop codons and amino acids reassigned in mitochondrial and nuclear genomes. Nonsense suppressor
tRNAs provided the raw material for nonsense codon reassignments, implying that the properties of the tRNA anticodon have
dictated the identity of nonsense codon reassignments.
Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
[Reviewing Editor: Dr. Laura Landweber] 相似文献
Mitochondrial tRNA import is widespread in eukaryotes. Yet, the mechanism that determines its specificity is unknown. Previous in vivo experiments using the tRNAs(Met), tRNA(Ile) and tRNA(Lys) have suggested that the T-stem nucleotide pair 51:63 is the main localization determinant of tRNAs in Trypanosoma brucei. In the cytosol-specific initiator tRNA(Met), this nucleotide pair is identical to the main antideterminant that prevents interaction with cytosolic elongation factor (eEF1a). Here we show that ablation of cytosolic eEF1a, but not of initiation factor 2, inhibits mitochondrial import of newly synthesized tRNAs well before translation or growth is affected. tRNA(Sec) is the only other cytosol-specific tRNA in T. brucei. It has its own elongation factor and does not bind eEF1a. However, a mutant of the tRNA(Sec) expected to bind to eEF1a is imported into mitochondria. This import requires eEF1a and aminoacylation of the tRNA. Thus, for a tRNA to be imported into the mitochondrion of T. brucei, it needs to bind eEF1a, and it is this interaction that mediates the import specificity. 相似文献
The universally conserved endoribonuclease P consists of one RNA subunit and, depending on its origin, a variable number of protein subunits. RNase P is involved in the processing of a large variety of substrates in the cell, the preferred substrate being tRNA precursors. Cleavage activity does not require the presence of the protein subunit(s) in vitro. This is true for both prokaryotic and eukaryotic RNase P RNA suggesting that the RNA based catalytic activity has been preserved during evolution. Progress has been made in our understanding of the contribution of residues and chemical groups both in the substrate as well as in RNase P RNA to substrate binding and catalysis. Moreover, we have access to two crystal structures of bacterial RNase P RNA but we still lack the structure of RNase P RNA in complex with its substrate and/or the protein subunit. Nevertheless, these recent advancements put us in a new position to study the way and nature of interactions between in particular RNase P RNA and its substrate. In this review I will discuss various aspects of the RNA component of RNase P with an emphasis on our current understanding of the interaction between RNase P RNA and its substrate. 相似文献
Ultrasound is defined as sound of a frequency that is too high for the human ear to detect—i.e. it is inaudible. Nevertheless this “silent sound” has a large range of applications in science, medicine and industry. The study of the effects of ultrasound on materials—known as sonochemistry—is one of the broadest and most exciting areas in current research. In this review some recent developments with major potential are identified from the fields environmental protection and materials processing.
Environmental protection can refer to methods of preventing pollution or to the removal of existing pollution. Here we will look at examples drawn from the latter in which ultrasound has been used for the purification of water (chemical and biological), the decontamination of the atmosphere and soil remediation i.e. the classic three domains of water, air and land.
In terms of materials processing two examples have been chosen, the treatment of sewage sludge and the control of crystallisation. In both of these cases it is predominantly the mechanical effects of acoustic cavitation, which produce the enhanced digestion, and dewatering of sludge and provide for the control in crystallisation processes. 相似文献
Pseudomonas aeruginosa is an opportunistic multi‐drug resistant pathogen implicated as a causative agent in nosocomial and community acquired bacterial infections. The gene encoding prolyl‐tRNA synthetase (ProRS) from P. aeruginosa was overexpressed in Escherichia coli and the resulting protein was characterized. ProRS was kinetically evaluated and the KM values for interactions with ATP, proline, and tRNA were 154, 122, and 5.5 μM, respectively. The turn‐over numbers, kcatobs, for interactions with these substrates were calculated to be 5.5, 6.3, and 0.2 s?1, respectively. The crystal structure of the α2 form of P. aeruginosa ProRS was solved to 2.60 Å resolution. The amino acid sequence and X‐ray crystal structure of P. aeruginosa ProRS was analyzed and compared with homologs in which the crystal structures have been solved. The amino acids that interact with ATP and proline are well conserved in the active site region and overlay of the crystal structure with ProRS homologs conforms to a similar overall three‐dimensional structure. ProRS was developed into a screening platform using scintillation proximity assay (SPA) technology and used to screen 890 chemical compounds, resulting in the identification of two inhibitory compounds, BT06A02 and BT07H05. This work confirms the utility of a screening system based on the functionality of ProRS from P. aeruginosa. 相似文献