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C B Mason

Publications and source records attributed to C B Mason.

6 recordsLinked to original sources
PubMed1997

Cloning and overexpression of two cDNAs encoding the low-CO2-inducible chloroplast envelope protein LIP-36 from Chlamydomonas reinhardtii.

Chlamydomonas reinhardtii, a unicellular green alga, grows photoautotrophically at very low concentrations of inorganic carbon due to the presence of an inducible CO2-concentrating mechanism. During the induction of the CO2-concentrating mechanism at low-CO2 growth conditions, at least five polypeptides that are either absent or present in low amounts in cells grown on high-CO2 concentrations are induced. One of these induced polypeptides with a molecular mass of 36 kD, LIP-36, has been localized to the chloroplast envelope. The protein was purified and the partial internal amino acid sequences were obtained through lys-C digestion. Two cDNAs encoding LIP-36 have been cloned using degenerate primers based on the amino acid sequences. The two genes encoding LIP-36 are highly homologous in the coding region but are completely different in the 5'-end and 3'-end untranslated regions. The deduced protein sequences show strong homology to the mitochondrial carrier protein superfamily, suggesting that LIP-36 is a chloroplast carrier protein. The regulation of the expression of these two genes at high- and low-CO2 growth conditions is also different. Both genes were highly expressed under low-CO2 growth conditions, with the steady-state level of LIP-36 G1 mRNA more abundant. However, neither gene was expressed at high-CO2 growth conditions. The gene products of both clones expressed in Escherichia coli were recognized by an antibody raised against LIP-36, confirming that the two cDNAs indeed encode the C. reinhardtii chloroplast envelope carrier protein LIP-36.

Amino Acid Sequence↗
PubMed1996

A low-CO2-inducible gene encoding an alanine: alpha-ketoglutarate aminotransferase in Chlamydomonas reinhardtii.

At low-CO2 (air) conditions, the unicellular green alga Chlamydomonas reinhardtii acquires the ability to raise its internal inorganic carbon concentration. To study this adaptation to low CO2, cDNA clones induced under low-CO2 growth conditions were selected through differential screening. One full-length clone is 2552 bp, with an open reading frame encoding 521 amino acids. The deduced amino acid sequence shows about 50% identity with alanine: alpha-ketogutarate aminotransferase (Ala AT, EC 2.6.1.2) from plants and animals, and the mRNA of this clone increased 4- to 5-fold 4 h after cells were switched from high-CO2 to low-CO2 growth conditions. The expression of the enzyme and its activity also increased accordingly at low-CO2 growth conditions. To study the physiological role of Ala AT, a pyridoxal phosphate inhibitor, aminooxyacetic acid, was added at 40 microM to the growth medium when cells were beginning to adapt to low CO2. This caused a 30% decrease in the maximum photosynthetic rate in air-adapting cells 8 h later. The addition of the inhibitor also caused the cells to excrete glycolate, a photorespiratory intermediate, but did not change the apparent affinity of the cell for external CO2. These physiological studies are consistent with the assumption that Ala AT is involved in the adaptation to low-CO2 conditions.

Adaptation, Biological↗
PubMed1991

Simplified Procedure for the Isolation of Intact Chloroplasts from Chlamydomonas reinhardtii.

A simple procedure that yields highly purified intact chloroplasts from Chlamydomonas reinhardtii is described. This procedure involves breakage of cell wall-deficient cells by passing them through a narrow bore syringe needle. The intact chloroplasts are then purified from the crude homogenate by differential centrifugation and Percoll gradient centrifugation. This procedure generates relatively high yields of chloroplasts capable of CO(2) fixation. These chloroplasts were characterized by electron microscopy, marker enzyme analysis, and ferricyanide exclusion. Transmission electron microscopy indicates that these chloroplasts retain their pyrenoids and eyespots. Scanning electron microscopy confirms that the characteristic cup shape of C. reinhardtii chloroplasts persists in vitro. This rapid, inexpensive procedure produces chloroplasts that should be useful for researchers studying the biochemistry and cell biology of C. reinhardtii chloroplasts.

Journal Article↗
PubMed1990

A New Chloroplast Protein Is Induced by Growth on Low CO(2) in Chlamydomonas reinhardtii.

The biosynthesis of a 36 kilodalton polypeptide of Chlamydomonas reinhardtii was induced by photoautotrophic growth on low CO(2). Fractionation studies using the cell-wall-deficient strain of C. reinhardtii, CC-400, showed that this polypeptide was different from the low CO(2)-induced periplasmic carbonic anhydrase. In addition, the 36 kilodalton polypeptide was found to be localized in intact chloroplasts isolated from low CO(2)-adapting cultures. This protein may, in part, account for the different inorganic carbon uptake characteristics observed in chloroplasts isolated from high and low CO(2)-grown C. reinhardtii cells.

Journal Article↗