ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.7678557

出版商:Wiley    

年代:1993

数据来源: WILEY

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.7678565

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

RNase P is an essential enzyme that is required for the biosynthesis of tRNA. It is composed of RNA and protein subunits. The RNA subunit of the enzyme derived from eubacterial sources can carry out the catalytic function by itself in vitro. Current studies of RNase P focus on structure‐function relationships with respect to interactions of the RNA subunit with its substrates and with respect to the determination of the kinetic parameters of the reaction, the role of the protein component, and the rules governing recognition of substrates.— Altman, S.; Kirsebom, L., Talbot, S. Recent studies of ribonuclease P.FASEB J.7: 7‐14; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.7916700

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Group I and group II introns are two types of RNA enzymes, ribozymes, that catalyze their own splicing by different mechanisms. In this review, we summarize current information about the structures of group I and group II introns, their RNA‐catalyzed reactions, the facilitation of RNA‐catalyzed splicing by protein factors, and the ability of the introns to function as mobile elements. The RNA‐based enzymatic reactions and intron mobility provide a framework for considering the role of primordial catalytic RNAs in evolution and the origin of introns in higher organisms.— Saldanha, R., Mohr, G., Belfort, M., and Lambowitz, A. M. Group I and group II introns.FASEB J.7: 15‐24; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.8422962

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

We describe the structures and catalytic properties of several naturally occurring self‐cleaving RNA motifs that give 2′, 3′ cyclic phosphate products. The hammerhead and hairpin motifs are derived from plant pathogenic RNAs and the delta motif is part of the human hepatitis delta element. A fourth motif fromNeurosporais less well characterized. By assembling the self‐cleaving RNAs from more than one oligoribonucleotide, the cleavage reaction can be examined under a variety of conditions and catalytic turnover can be demonstrated. Mutagenesis and chemical methods to introduce modified nucleotides allowed the structural requirements to be deduced. The role of divalent cations in the catalytic mechanism is discussed.— Long, D. M., and Uhlenbeck, O. C. Self‐cleaving catalytic RNA.FASEB J.7: 25‐30; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.8422971

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Three well‐characterized RNA catalysts not only require Mg2+for activity, but also bind a metal ion (or ions) within the active site, apparently in a catalytic rather than solely structural role. I suggest, in view of the general catalytic utility of bound ions, that catalytic RNAs be viewed as Cheshire cats, by dimming their complex three‐dimensional ribonucleotide structure to leave only the sharp mineral parts in view. That is, catalytic RNAs may be viewed as metalloenzymes, with the burdens of catalysis frequently borne by specifically poised metal ions. Comparison to modern protein metalloenzymes predicts particular RNA metallocatalysts that may be possible presently, and in a hypothetical ancestral RNA world that did not encode peptide catalysts. In support of this view, known catalytic RNAs can be considered Cheshire catalysts; that is, they have apparent cognates among the protein metalloenzymes.— Yarus, M. How many catalytic RNAs? Ions and the Cheshire cat conjecture.FASEB J.7: 31‐39; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.8422972

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Messenger RNA maturation in eukaryotes typically involves the removal of introns from long precursor molecules. An unusual form of RNA splicing in which separate precursor transcripts contribute sequences to the mature mRNA through intermolecular reactions has now been documented in a number of diverse organisms. In this review, the phenomenon of pre‐mRNAtrans‐splicing has been divided into two categories. The “spliced leader” type, found in protozoans such as trypanosomes and lower invertebrates such as nematodes, results in the addition of a short, capped 5′ noncoding sequence to the mRNA. The “discontinuous group II intron” form oftrans‐splicing, found in plant/algal chloroplasts and plant mitochondria, involves the joining of independently transcribed coding sequences, presumably through interactions between “intronic” RNA pieces. Both categories oftrans‐splicing are mechanistically similar to conventional nuclear pre‐mRNAcis‐splicing; potential evolutionary relationships are discussed.— Bonen, L.Trans‐splicing of pre‐mRNA in plants, animals, and protists.FASEB J.7: 40‐46; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.8422973

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Ribonucleoproteins (RNPs) play essential roles in many aspects of gene expression. Two families of) nuclear RNPs are involved in the processing of primary transcripts made by RNA polymerases I and II (pol I and II), two of the three polymerases present in the nuclei of eukaryotic cells. Ribosomal RNA precursor transcription by pol I, subsequent processing of the precursor, and the initial steps of ribosome assembly all take place in the nucleolus. A group of nucleolar RNPs containing small RNAs (small nucleolar RNAs or snoRNAs) are involved in the posttranscriptional nucleolar events of ribosome biosynthesis. Six members of a related family of small nuclear RNAs (snRNAs) are required for the processing of mRNA precursors in the nucleoplasm. Five of these snRNAs (U1, U2, U4‐6) participate in the removal of intervening sequences while the sixth (U7) plays an essential role in the 3′ processing of a subset of mRNA precursors, the histone pre‐mRNAs. This is a review of structural and functional aspects of the U1‐U7 snRNAs and of snoRNAs.— Mattaj, I. W., Tollervey, D., and Séraphin, B. Small nuclear RNAs in messenger RNA and ribosomal RNA processing.FASEB J.7: 47‐53; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.8422974

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

RNA editing in the mitochondrion of kinetoplastid protozoa results in the posttranscriptional addition and deletion of uridine residues in mRNAs. Editing of mRNAs can lead to the formation of initiation codons for mitochondrial translation, the correction of frame‐shifted genes at the RNA level, and in extensively edited mRNAs, the formation of complete reading frames. Kinetoplastid RNA editing requires that genetic information from two or more separately transcribed genes be brought together to form the mature, edited mRNA. The information necessary for the proper insertion or deletion of uridines in the mRNA is present in small mitochondrial transcripts termed guide RNAs (gRNAs). Editing of mRNAs appears to be associated with a high molecular weight complex, called the editosome, containing specific gRNAs, unedited mRNAs, and proteins. Editing is likely a two‐step process involving first the breakage of a phosphodiester bond at the editing site and formation of a chimeric molecule with a gRNA covalently joined to the 5′ end of the 3′ portion of an mRNA. The chimera is resolved by the rejoining of the 5′ end of the mRNA to the 3′ portion of the mRNA with the addition or deletion of a uridine at the junction point. Two models are proposed for the biochemical mechanism of RNA editing. The first is an enzymatic cascade of cleavage and ligation while the other supports successive rounds of transesterification. The obvious functional necessity for editing in kinetoplastid mitochondria is the formation of translatable mRNAs. Far less clear is the evolutionary origin of editing and the role editing plays in regulating mitochondrial gene expression.— Hajduk, S. L., Harris, M. E., and Pollard, V. W. RNA editing in kinetoplastid mitochondria.FASEB J.7: 54‐63; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.8422975

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

In the mitochondria and chloroplasts of flowering plants (angiosperms), transcripts of protein‐coding genes are altered after synthesis so that their final primary nucleotide sequence differs from that of the corresponding DNA sequence. This posttranscriptional mRNA editing consists almost exclusively of C‐to‐U substitutions. Editing occurs predominantly within coding regions, mostly at isolated C residues, and usually at first or second positions of codons, thereby almost always changing the amino acid from that specified by the unedited codon. Editing may also create initiation and termination codons. The net effect of C‐to‐U RNA editing in plants is to make proteins encoded by plant organelles more similar in sequence to their nonplant homologs. In a few cases, a strong argument can be made that specific C‐to‐U editing events are essential for the production of functional plant mitochondrial proteins. Although the phenomenon of RNA editing in plants is now well documented, fundamental questions remain to be answered: What determines the specificity of editing? What is the biochemical mechanism (deamination, base exchange, or nucleotide replacement)? How did the system evolve? RNA editing in plants, as in other organisms, challenges our traditional notions of genetic information transfer.— Gray, M. W.; Covello, P. S. RNA editing in plant mitochondria and chloroplasts.FASEB J.7: 64‐71; 1993.

ISSN:0892-6638    

DOI:10.1096/fasebj.7.1.8422976

出版商:Wiley    

年代:1993

数据来源: WILEY