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M D Morch

Publications and source records attributed to M D Morch.

14 recordsLinked to original sources
PubMed1989

Proteolytic origin of the 150-kilodalton protein encoded by turnip yellow mosaic virus genomic RNA.

Turnip yellow mosaic virus genomic RNA codes in vitro for two overlapping proteins, 150-kilodalton (150K protein) and 206-kilodalton (206K protein) proteins. The proteolytic maturation known to affect the 206K protein has been further characterized by in vitro translation assays in a reticulocyte lysate or wheat germ extract. Cleavage is inhibited at 37 degrees C and restored when the temperature is shifted to 30 or 25 degrees C. Temperature shift experiments are used here to demonstrate that the 150K protein and the previously characterized 78K protein are the two fragments resulting from a primary cleavage phenomenon that affects the 206K protein in a cotranslational manner under usual translation conditions. This processing is prevented by several cysteine and serine proteinase inhibitors.

Gene Expression↗
PubMed1988

Phospholipid transfer protein: full-length cDNA and amino acid sequence in maize. Amino acid sequence homologies between plant phospholipid transfer proteins.

We have determined the primary structure of a phospholipid transfer protein (PLTP) isolated from maize seeds. This protein consists of 93 amino acids and shows internal homology originating in the repetition of (do)decapeptides. By using antibodies against maize PLTP, we have isolated from a cDNA library one positive clone (6B6) which corresponds to the incomplete nucleotide sequence. Another cDNA clone (9C2) was obtained by screening a size-selected library with 6B6. Clone 9C2 (822 base pairs) corresponds to the full-length cDNA of the phospholipid-transfer protein whose mRNA contains 0.8 kilobase. Southern blot analysis shows that the maize genome may contain several PLTP genes. In addition, the deduced amino acid sequence of clone 9C2 reveals the presence of a signal peptide. The significance of this signal peptide (27 amino acids) might be related to the function of the phospholipid-transfer protein. The amino acid sequence of maize PLTP was compared to those isolated from spinach leaves or castor bean seeds which exhibit physicochemical properties close to those of the maize protein. A high homology was observed between the three sequences. Three domains can be distinguished: a highly charged central core (around 40-60), a very hydrophobic N-terminal sequence characteristic of polypeptide-membrane interaction, and a hydrophilic C terminus. A model for plant phospholipid-transfer proteins is proposed in which the phospholipid molecule is embedded within the protein with its polar moiety interacting with the central hydrophilic core of the protein, whereas the N-terminal region plunges within the membrane in the transfer process.

Amino Acid Sequence↗
PubMed1988

Ionic conditions for the cleavage of the tRNA-like structure of turnip yellow mosaic virus by the catalytic RNA of RNase P.

The 3'-end of the RNA genome of turnip yellow mosaic virus can form a pseudoknotted tRNA-like structure that can be recognized by several tRNA-specific enzymes. We have found that the catalytic RNA component of Bacillus subtilis RNase P can cleave this structure in unusually low ionic strength buffers at a site analogous to the 5'-end of an aminoacyl stem of a tRNA. Most other precursors can only be processed under low ionic strength conditions if the RNase P holoenzyme is used; processing by the catalytic RNA component alone requires a higher ionic strength buffer. The cleavage of the turnip yellow mosaic virus tRNA-like structure demonstrates the importance of the substrate in determining the optimal buffer conditions for this reaction and also shows that high ionic strength buffers are not always necessary for cleavage by the catalytic RNA.

Ammonium Chloride↗
PubMed1988

Stop making sense: or Regulation at the level of termination in eukaryotic protein synthesis.

An increasing number of examples of translational regulation at the level of termination has been recently reported in eukaryotes. This paper reviews our present knowledge on this topic and proposes an understanding of these regulations by relating the study of viral gene expression to a comprehensive view of the mechanisms and components of the translational process.

Animals↗
PubMed1988

Overlapping open reading frames revealed by complete nucleotide sequencing of turnip yellow mosaic virus genomic RNA.

The complete nucleotide sequence of turnip yellow mosaic virus (TYMV) genomic RNA has been determined on a set of overlapping cDNA clones using a sequential sequencing strategy. The RNA is 6318 nucleotides long, excluding the cap structure. The genome organization deduced from the sequence confirms previous results of in vitro translation. A novel open reading frame (ORF) putatively encoding a Pro-rich and very basic 69K (K = kilodalton) protein is detected at the 5' end of the genome. It is initiated at the first AUG codon on the RNA and overlaps the major ORF that encodes the non structural 206K (previously referred to as 195K) protein of TYMV; its function is unknown. Several amino acid consensus sequences already described among plant and animal viruses are also found in the TYMV-encoded polypeptides. A comparison with other viruses whose RNA sequence is known leads to the conclusion that TYMV belongs to the "Sindbis-like" supergroup of viruses and could be related to Semliki forest virus.

Amino Acid Sequence↗
PubMed1988

Plant viruses and new perspectives in cross-protection.

Cross-protection in plants is the phenomenon whereby a plant preinoculated with a mild virus strain becomes resistant to subsequent inoculation by a related severe strain. It has been used on a large scale in cases where no resistant plants are available. Although several hypotheses have been proposed to explain the molecular mechanism underlying cross-protection, no single hypothesis can account for all the data obtained. Recently, a phenomenon akin to cross-protection has been achieved in transformed plants harboring the cDNA of a part of a viral RNA genome. These results obtained by genetic engineering raise new hopes for obtaining plants resistant to virus infection.

Genetic Engineering↗
PubMed1987

A new 'sense' RNA approach to block viral RNA replication in vitro.

The use of "antisense" RNA is being widely considered to block specific steps in viral infection. We propose here a new "sense" RNA approach to block viral RNA replication in vitro and possibly in vivo. In the turnip yellow mosaic virus (TYMV) system, the recognition site of the viral replicase (RNA-dependent RNA polymerase) is assumed to be located within the 3' end of the RNA genome. Small "sense" RNAs have been obtained by in vitro transcription of the corresponding cloned cDNAs. Replication of TYMV RNA in vitro is shown here to be blocked only by those RNAs that contain the 3' terminal region of the genome.

Antiviral Agents↗
PubMed1987

Novel amber suppressor tRNAs of mammalian origin.

Two amber suppressor tRNAs have been isolated from calf liver. They are different from previously identified naturally occurring amber suppressors of eukaryotes in so far as they are neither tRNATyr nor tRNAGln. They are leucine iso-acceptors and their nucleotide sequence indicates that they harbour a CAA and a CAG anticodon respectively. Both species are functional as amber suppressors as demonstrated by readthrough of the amber codon which terminates the 126 kd protein gene of tobacco mosaic virus RNA. The results bring new information in the discussion of codon-anticodon recognition and regulation of termination in eukaryotic protein synthesis.

Animals↗
PubMed1983

Comparison of three different cell-free systems for turnip yellow mosaic virus RNA translation.

The two proteins of molecular weights 150,000 and 195,000 specific of turnip yellow mosaic virus (TYMV) RNA translation in reticulocyte lysates have now also been detected in two other cell-free systems programmed with TYMV RNA: the wheat germ extract and the Ehrlich ascites cell-free system. The wheat germ extract contains proteases that affect the nascent TYMV polypeptide chains. The specific post-translational maturation of the protein of molecular weight 195,000 known to occur in the reticulocyte lysate has been investigated in the ascites system. An N-terminal fragment and a C-terminal fragment of molecular weights 120,000 and 78,000, respectively, could be detected co-migrating with the post-translational cleavage products observed in the reticulocyte lysate. Similarly, a C-terminally labelled 78,000 molecular weight fragment could be observed in the wheat germ system. The differences between the three in vitro systems with respect to TYMV RNA translation are discussed.

Animals↗
PubMed1983

[Not Available].

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Genetics↗
PubMed1982

Proteolytic maturation of the turnip-yellow-mosaic-virus polyprotein coded in vitro occurs by internal catalysis.

The genomic RNA of turnip yellow mosaic virus is translated in vitro into two major high-molecular-weight proteins, the larger of which (Mr 195 000) undergoes post-translational cleavage. The mechanism of formation of the primary cleavage products (Mr 120 000 and Mr 78 000) of the 195 000-Mr protein has been examined. The fact that cleavage partly occurs at a rate insensitive to dilution of the 195 000-Mr protein is suggestive of an intramolecular mechanism of proteolytic maturation.

Genes, Viral↗
PubMed1980

Polyamines stimulate suppression of amber termination codons in vitro by normal tRNAs.

Polyamines, such as spermine and spermidine, are able to stimulate reading of amber termination codons on viral messenger RNAs in vitro. This phenomenon is not due to an overall increase of error frequency during translation, but to a specific effect on a normal tRNA that is present in various eukaryotic cell preparations. The enhancement of reading of termination codons by normal tRNAs should be of major importance for the expression of specific genes in eukaryotic cells.

Animals↗
PubMedDate not supplied

Multiple alignment and hierarchical clustering of conserved amino acid sequences in the replication-associated proteins of plant RNA viruses.

We have used multiple alignment computer programs to align and hierarchically cluster the conserved amino acid "signature" sequences found in the replication-associated proteins of all plant RNA viruses sequenced so far. These regions, called "polymerase", "nucleotide-binding" and "N-terminal" are well conserved even between viruses which are only distantly related, and are thus very well suited for this type of analysis. Our results show that the clusterings obtained using these very short amino acid sequences are very robust to computing parameters and are surprisingly well matched with the taxonomic grouping of RNA plant viruses. The possibility of using this system as a new taxonomic criterion is discussed.

Amino Acid Sequence↗