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M P Staves

Publications and source records attributed to M P Staves.

11 recordsLinked to original sources
PubMed1992

The contribution of the extracellular matrix to gravisensing in characean cells.

The cell-extracellular matrix junction, which includes the cell wall and the outer surface of the plasma membrane, may be an essential region for the perception of gravity by the internodal cells of Chara corallina. Typically, when an internodal cell is oriented vertically, the downwardly directed cytoplasmic stream travels at a velocity that is 10% faster than that of the upwardly directed stream. However when the cells are treated with impermeant hydrolytic enzymes that partially digest cellulose or hemicellulose, the cells lose their ability to respond to gravity even though streaming continues. By contrast, enzymes that digest pectins have no effect on the gravity-induced polarity of cytoplasmic streaming. Furthermore, gravisensing is sensitive to protease treatment; Proteinase K, thermolysin and collagenase but not trypsin, alpha-chymotrypsin or carboxypeptidase B, inhibit gravisensing. These findings indicate that proteins in the cell-extracellular matrix junction may be required for gravisensing. Moreover, the tetrapeptide Arg-Gly-Asp-Ser (RGDS) inhibits gravisensing in a concentration-dependent manner, indicating that the gravireceptor may be an integrin-like protein. The macromolecules necessary for gravisensing have been localized to the cell ends. As a consequence of the exoplasmic site of action of the enzymes and the tetrapeptides, we interpret the results to mean that they are acting on the gravireceptor, although we cannot eliminate the possibility that they are acting on the signal transduction chain. On the whole, our observations indicate that the cell-extracellular matrix junction is a sine qua non for graviperception in statolith-free Chara internodal cells and we suggest that the gravireceptor is located in this region.

Amino Acid Sequence↗
PubMed1991

Stereoselective, nonenzymatic, intramolecular transfer of amino acids.

Biological systems synthesize proteins with an almost exclusive use of L-amino acids and virtually none of the D isomer. There has been no satisfactory explanation for the origin of this use of the L isomer. Research presented here shows that at pH 5, transfer of phenylalanine from the adenylate anhydride to ester occurs and is 95-97% efficient for the L isomer and only about 50% efficient for the D isomer. The origin of the use of the L isomer, given D-ribose nucleotides, may be based in part on this stereoselectivity.

Adenosine Monophosphate↗
PubMed1991

Stereoselective formation of bis(alpha-aminoacyl) esters of 5'-AMP suggests a primitive peptide synthesizing system with a preference for L-amino acids.

In the biosynthesis of proteins, each amino acid passes from the aminoacyl adenylate to become an amino acid ester and finally a 2' (3') peptidyl ester of the AMP residue at the end of a tRNA. Consequently, the chemistry of protein synthesis is the chemistry of aminoacyl and peptidyl AMP. Our data has revealed properties of 5'-AMP and its esters which should allow the preferential catalytic synthesis of L-amino acid peptides via a bis(2', 3'-aminoacyl) ester intermediate. Results in this paper concern one step in the proposed process and show that preexisting Ac-L-Phe monoester reacts about 2.5-times faster to form diester than preexisting Ac-D-Phe monoester.

Adenosine Monophosphate↗
PubMed1990

Was there a universal tRNA before specialized tRNAs came into existence?

It is generally true that evolving systems begin simply and become more complex in the evolutionary process. For those who try to understand the origin of a biochemical system, what is required is the development of an idea as to what simpler system preceeded the present one. Here we present an hypothesis that a universal tRNA molecule, capable of reading many codons may have preceeded the appearance of individual tRNAs. Evidence seems to suggest that this molecule may have been derived from a common ancestor of the contemporary 5S rRNAs and tRNAs.

Biological Evolution↗
PubMed1990

Ribonucleic acids may be catalysts for the preferential synthesis of L-amino acid peptides: a minireview.

This minireview is a summary of the basic concepts and pieces of experimental evidence supporting a hypothesis that suggests a mechanism whereby purine monoribonucleotides having D-ribose may be able to preferentially catalyze the synthesis of L-amino acid peptides. The proposed mechanism involves a 2'-3' diaminoacyl intermediate and the preference accrues from several factors that favor the L-isomer, principally for hydrophobic amino acids. Although the hypothesis has not been fully tested, some crucial evidence has been published. Other pieces of evidence are now being submitted or are in press for publication and still other experiments, principally on the step of peptide bond formation, are in the process of being carried out. The purpose of a review at this point is to present the hypothesis to the scientific community in hopes of generating discussion, suggestions, and evaluation by other workers. Should the hypothesis prove correct, it may represent the most primitive and fundamental relationship between the nucleic acid and protein systems. In addition, it would represent another important example of the catalytic ability of RNA.

Amino Acids↗
PubMed1989

tRNA-rRNA sequence matches from inter- and intraspecies comparisons suggest common origins for the two RNAs.

1. Comparisons were made of the results of searches within and among different species of organisms for sequence matches between transfer RNAs and ribosomal RNAs. The purpose was to determine whether the matching sequences might result from selection acting on the two RNAs within a common cellular environment. 2. The results indicate that most matches do not reflect such selection. The matches described were more frequent than those found in searches among randomized sequences and the frequency of intraspecific matches was not significantly higher than that of interspecific matches. 3. The matches are thought to identify conserved vestiges of a molecule or molecules ancestral to both classes of RNAs (Bloch, D.P., McArthur, B. and Mirrop, S. (1985). BioSystems, 17: 209-225). The matching sequences are interpreted as homologies.

Anticodon↗
PubMed1988

Evolution of E. coli tRNA(Trp).

Earlier studies (1) have shown there are direct correlations between the hydrophobicity ranking of most amino acids and their anticodonic nucleotides. However, four anticodonic assignments, i.e. those for Trp, Tyr, Ile and the XGA anticodons for Ser, did not correlate. It was our proposal that this failure to correlate was due to the fact that these assignments were made late, relative to the bulk of the assignments, in evolution through the mutation of existing tRNAs. We have shown (2) that E. coli tRNA(Ile 1) and tRNA(Ile 2) were likely derived from tRNA(Val 1) and tRNA(Lys) respectively and E. coli tRNA(Tyr) was possibly derived from E. coli 5s rRNA or a common precursor with 5s rRNA (3). The fact that quite high homologies were observed in these comparisons is consistent with the late evolution of the tRNAs in question. We now examine the evolution of E. coli tRNA(Trp) by comparing its homology with other E. coli tRNAs. The data suggest a possible evolutionary relationship with E. coli tRNA(Gly) or tRNA(Arg). The data support the idea of the late assignment of anticodons to Trp.

Anticodon↗
PubMedDate not supplied

Evolution of E. coli tRNA(Ile): evidence of derivation from other tRNAs.

Two E. coli tRNA(Ile) sequences were compared against those of 36 other E. coli tRNAs. tRNA(Ile) 1 was found to bear high similarity with tRNA(Val) 1 (E = 1.11 X 10(-18] while tRNA(Ile) 2 had the greatest match (E = 3.40 X 10(-19] with tRNA(Lysl) (E is the expected number of such matches, per search, based on coincidence). These matches, which we consider to represent homologies, extend from base 7 to base 67 in the former and base 7 to the end (76) in the latter pair. These results coupled with others on the lower activity of isoleucine in reactions postulated to be important in primitive protein synthesis (i.e., esterification reactions and non-enzymatic activation by ATP [1-3]) lead us to propose that isoleucine was included among the proteinaceous amino acids, and received its anticodonic assignment, relatively late in evolution through mutation of tRNAs previously employed for other amino acids.

Base Sequence↗
PubMedDate not supplied

Demonstrating evolutionary relationships between macromolecular sequences through mutual relationships with a third sequence.

Corresponding sites of the Euglena chloroplast and yeast small subunit ribosomal RNAs (rRNAs) show only an insignificant match with each other but show extensive matches with Euglena chloroplast tRNA(arg). The match with the tRNA extends farther toward the 5' end of the Euglena rRNA and toward the 3' end of the yeast rRNA. The expected number of such configurations given the number of RNAs searched is about 1 in 100,000. Comparison of two sequences with a third sequence frequently reveals relationships where pairwise comparisons fail to do so.

Animals↗
PubMedDate not supplied

On the probability of a common origin for tRNA and 5S rRNA.

As part of a continuing study on the origin of genetic coding and the process of protein synthesis, we have compared sequences of a large number of transfer RNAs and several 5S ribosomal RNAs using automated routines. Transfer RNAs were found to exhibit a high degree of matching with 5S rRNAs. These matches are considered to be indicative of sequence homology, reflecting common ancestry of the two molecules. Other possible explanations for the matches (convergence, transfection) are discussed and found to be highly implausible. Matches are also found between 5S rRNA and the introns of yeast precursor tRNAs. Many matches extend from before the 3' end to after the 5' end of circularized 5S rRNA sequences. Data is presented which indicates a tandemly duplicated or circular molecule could have served as the precursor to both 5S rRNA and tRNA. A derivative of this molecule may have functioned as a universal translator before the evolution of the highly specialized tRNAs.

Animals↗