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D P Weeks

Publications and source records attributed to D P Weeks.

32 records · Page 2Linked to original sources
PubMed1978

Selective inhibition of tubulin synthesis by amiprophos methyl during flagellar regeneration in Chlamydomonas reinhardi.

Amiprophos methyl (APM) is a strong, readily reversible and highly selective inhibitor of tubulin synthesis in Chlamydomonas reinhardi. The extensive induction of tubulin synthesis that accompanies flagellar regeneration in this organism is prevented by 3 to 10 micrometerAPM. When applied after induction has begun, APM causes a rapid cessation of tubulin synthesis. Translation studies in vitro indicate that the lack of tubulin production in APM-treated cells is not due to a direct inhibition of tubulin messenger RNA translation but rather to a selective depletion of tubulin messenger RNA.

Chlamydomonas↗
PubMed1976

Induction of microtubule protein synthesis in Chlamydomonas reinhardi during flagellar regeneration.

Flagellar regeneration in gametes of Chlamydomonas reinhardi is initiated within 15-20 min after flagellar amputation and proceeds at a rapid but decelerating rate until by 90 min flagellar outgrowth in 80-85% complete. Sufficient flagellar protein reserves exist in the cytoplasm to allow regeneration of flagella 1/3-1/2 normal length. Nevertheless, in vivo labeling with 14C-amino acids shows that microtubule protein and other flagellar proteins are synthesized de novo during flagellar regeneration. To determine whether tubulin is synthesized continuously by gametic cells or whether its synthesis is induced as a consequence of deflagellation, we have isolated polyribosomes from deflagellated and control cells, and analyzed the proteins produced by these polyribosomes during in vitro translation. Two proteins of 53,000 and 56,000 molecular weight which co-migrate with flagellar and chick brain tubulin on SDS-polyacrylamide gels and which selectively co-assemble with chick brain tubulin during in vitro microtubule assembly are synthesized by polyribosomes (or polyadenylated mRNA) from deflagellated cells. No microtubule proteins can be detected in the translation products synthesized by polyribosomes (or mRNA) from control cells, clearly indicating that deflagellation results in the induction ot tubulin synthesis. Kinetics of tubulin synthesis demonstrate that induction takes place immediately after deflagellation; polyribosomes bearing tubulin mRNA can be detected in the cytoplasm in as little as 15 min after removal of flagella. Maximal rates of tubulin synthesis occur between 45 and 90 min after deflagellation when approximately 14% of the protein being synthesized by the cell is tubulin. This estimate of tubulin synthesis based on in vitro translation data agrees well with in vivo measurements of flagellar tubulin synthesis. While high levels of tubulin production extend well beyond the period of rapid flagellar assembly, synthesis begins to decline after 90 min, and by 180 min after deflagellation only low levels of tubulin mRNA are detectable in polyribosomes.

Chlamydomonas↗
PubMed1970

Aurintricarboxylic acid and initiation factors of wheat embryo.

In extracts of wheat embryo, aurintricarboxylic acid inhibits attachment of ribosomes to messenger RNA and has little effect on aminoacyl transfer to peptide. This specificity of inhibition allows (i) the demonstration that the initial phase of amino acid incorporation dependent on RNA of tobacco mosaic virus involves an "initiation" reaction between ribosome and messenger RNA which requires two soluble factors, (ii) an assay facilitating purification of the initiation factors, and (iii) the demonstration that these factors are distinct from aminoacyl transfer enzymes.

Amino Acids↗
PubMed1970

Protein chain initiation by methionyl-tRNA in wheat embryo.

The mechanism of protein chain initiation has been investigated in a cell-free amino acid incorporation system from wheat embryos dependent on tobacco mosaic virus RNA. Analysis of the N-termini of the labeled peptide products of short-term incubations showed the presence of unblocked methionine. In addition, methionyl-tRNA (Met-tRNA) could be bound to ribosomes at 1.3 mM Mg(++) in a reaction requiring viral RNA, ATP, GTP, and soluble protein factors. Incorporation experiments with the two cytoplasmic Met-tRNAs of wheat germ, an initiating species designated Met-tRNA(i) and a Met-tRNA(m), showed that methionine transfer from Met-tRNA(i) was linear from zero time, while that from Met-tRNA(m) occurred only after an appreciable lag. Analysis of the peptide products showed that methionine transfer from Met-tRNA(i) was predominantly N-terminal. In contrast, methionine transfer from Met-tRNA(m) was exclusively into internal positions. Similar selectivity was observed in the ribosome binding assay; only Met-tRNA(i) showed a strong reaction. These experiments provide strong evidence that in the wheat embryo, cytoplasmic Met-tRNA(i) functions without formylation in the initiation of protein synthesis.

Amino Acids↗
PubMed1969

Polyribosome isolation in the presence of diethyl pyrocarbonate.

Isolation of polyribosomes from wheat embryos and corn root tips in the presence of diethyl pyrocarbonate showed this reagent to have a protective effect on polyribosome structure. In addition, the use of diethyl pyrocarbonate allowed initial homogenization to be performed under less stringent conditions than those normally employed for polyribosome isolation. The use of the reagent is however limited, in that it is deleterious to in vitro ribosomal amino acid incorporation.

Amino Acids↗