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Papers by Gabriel Philippe

Plant Molecular Biology, 1992

The complete amino acid sequences of two variants of histone H2B of maize were deduced from the c... more The complete amino acid sequences of two variants of histone H2B of maize were deduced from the cDNAs isolated from a maize cDNA library. The two encoded proteins are 150 (H2B(1)) and 149 (H2B(2)) amino acids long and shows the classical organization of H2B histones. The hydrophobic C-terminal region is highly conserved as compared to that of the animal counterparts with only 21 changes (13 conservative) among the 90 residues. Between the N-terminal part and the C-terminal region we note the presence of a basic cluster (9 residues) characteristic of histones H2B. The N-terminal third is extended as compared to the animal consensus H2B and has the same size as the H2B histone of wheat. Up to 9 acidic residues and a five time repeated pentapeptide PA/KXE/KK are present in this region. Southern-blot hybrization showed that the H2B histones are encoded by a multigenic family like the other core histones (H3 and H4) of plants. The general expression pattern of these genes was not significantly different from that of the H3 and H4 genes neither in germinating seeds nor in different tissues of adult maize.

Biochimica Et Biophysica Acta (bba) - Nucleic Acids and Protein Synthesis, 1976

Phosphodiesterase I from the venom of Bothrops atrox has been purified by successive chromatograp... more Phosphodiesterase I from the venom of Bothrops atrox has been purified by successive chromatography on phosphocellulose P-11, hydroxyapatite, and DEAE-cellulose DE 52. The final product gave a single band on sodium dodecylsulfate-polyacrylamide gels and was free of endonuclease, 5'-nucleotidase, and unspecific alkaline phosphatase activity. It was concentrated in an Amicon ultrafiltrator without loss of activity and could be stored in 10 mM magnesium acetate and 10% glycerol at 4°C for at least a year. Under optimal conditions, the enzyme reaction requires 15 mM Mg 2÷ and a pH of 9.2. Phosphodiesterase I is relatively thermostable and, in the presence of a macromolecular substrate, was not denatured after 4 h at 55°C. The pure enzyme offers new possibilities for sequence studies on highly structured nucleic acids at elevated temperatures.

Biochimie, 1993

The primary structure of the plant histone genes has been deduced from the comparison of the nucl... more The primary structure of the plant histone genes has been deduced from the comparison of the nucleotide sequences of 23 genes and 14 cDNAs from eight different species. These data confirmed the extreme conservation of histones H3 and H4 in plant and animal kingdoms. Histone H2B is more variable than H2A and the histone H1 is the less conserved histone. Some interesting observations concerning the non-conserved regions of H2A and H2B in their extended C- and N-terminal regions are reported. Only three plant histone genes were found to possess intervening sequences: one H1 gene and two H3.3 like genes. The most striking differences found between the two kingdoms are the absence from plant histone genes of the palindromic structure existing downstream of the animal genes and the fact that plant histone mRNAs are polyadenylated. This suggests that the post-transcriptional regulation of expression of histone genes is different in the two kingdoms. In plants the multiple copies of the histone genes are organized into multigenic families. In the complex genome of maize the multiple copies of the genes are highly dispersed on the genome.

Plant Molecular Biology, 1993

The complete amino acid sequence of a cytoplasmic ribosomal protein S13 of maize was deduced from... more The complete amino acid sequence of a cytoplasmic ribosomal protein S13 of maize was deduced from the cDNA isolated from a maize cDNA library. The encoded protein is 151 amino acids long and shows a homology of 73% with the corresponding protein S13 of rat. Southern blots analysis shows that the maize protein S13 is encoded by a small multigene family conserved in plant species closely related to maize. The S13 RNAs accumulate preferentially in proliferating tissues and cells and their transcription occurs in parallel to the DNA synthesis.

Ribonucleotide reductase (RNR) is a key enzyme involved in the DNA synthesis pathway. The RNR-enc... more Ribonucleotide reductase (RNR) is a key enzyme involved in the DNA synthesis pathway. The RNR-encoded genes are cell cycle regulated and specifically expressed in S phase. The promoter of the RNR2 gene encoding for the small subunit was isolated from tobacco. Both in vivo and in vitro studies of the DNA-protein interactions in synchronized BY2 tobacco cells showed that two E2F-like motifs were involved in multiple specific complexes, some of which displayed cell cycle-regulated binding activities. Moreover, these two elements could specifically interact with a purified tobacco E2F protein. Involvement of the E2F elements in regulating the RNR2 promoter was checked by functional analyses in synchronized transgenic BY2 cells transformed with various RNR2 promoter constructs fused to the luciferase reporter gene. The two E2F elements were involved in upregulation of the promoter at the G1/S transition and mutation of both elements prevented any significant induction of the RNR promoter. In addition, one of the E2F elements sharing homology with the animal E2F/cell cycle-dependent element motif behaved like a repressor when outside of the S phase. These data provide evidence that E2F elements play a crucial role in cell cycle regulation of gene transcription in plants.

Developmental Genetics, 1987

The general structure of the plant histone genes has been deduced from the comparison of the nucl... more The general structure of the plant histone genes has been deduced from the comparison of the nucleotide sequences of ten H3 and H4 genes of maize (3 H3 and 3 H4) and Arabidopsis thaliana (2 H3 and 2 H4). The five H3 and five H4 genes encode the same proteins, respectively. The 5′-flanking regions contain the classical histone gene-specific consensus sequences. In addition, a conserved octanucleotide CGCGGATC was found in all plant histone genes at 200–250 nucleotides before the initiation codon.All six maize H3 and H4 genes are transcribed during early germination as shown by nuclease S1 mapping and reverse transcriptase primer extension experiments. The mRNA 5′-ends are located within the consensus sequence CCAA/CT/C. The 3′-ends lack the classical T-hyphenated dGC-rich palindromic structure and possess long nontranslated sequences.In both plants the multiple copies of the H3 and H4 genes are organized into multigenic families. The genes of each family show a similar proximal environment, suggesting that they originate from the duplication of a common ancestor.

Plant Molecular Biology, 1991

The steady-state levels of H3 and H4 mRNAs transcribed from three H3 and two H4 multigene subfami... more The steady-state levels of H3 and H4 mRNAs transcribed from three H3 and two H4 multigene subfamilies were studied during germination and in different organs of maize. During germination the five subfamilies are expressed in parallel to DNA synthesis, but a 5-fold difference in the quantity of mRNAs transcribed per gene copy was found from our subfamily to another. In adult plants H3 and H4 mRNA levels are highest in organs containing meristematic tissues but also high in non-proliferating tissues. No strict tissue specificity expression could be detected but some subfamilies show preferential expression in some tissues.

Plant Molecular Biology, 1983

Histones were extracted from purified nuclei isolated from four cereals,viz. barley (Hordeum vulg... more Histones were extracted from purified nuclei isolated from four cereals,viz. barley (Hordeum vulgare), wheat(Triticum aestivum), Aegilops squarrosa and corn (Zea mais), and from tobacco (Nicotiana tabacum). Analysis of the histones on SDS gels showed complex electrophoretic patterns with one species of both H3 and H4, one to three species of H1 and two to five species of H2. Judged from the electrophoretic patterns, the histones from barley, wheat and Aegilops are identical but different from those of corn with respect to H2. Like tobacco, corn showed two H2 components, whereas barley, wheat and Aegilops showed five H2 components. SDS gel electrophoresis of histones extracted from buds and roots of germinating seeds at different steps of germination and from different parts of ten-day-old leaves revealed that the existence in barley of multiple histone 2 variants is not restricted to any particular stage of differentiation of barley. Histones from barley leaves were resolved into four fractions by Biogel P-100 gel filtration and histones 2 were further fractionated by their differential solubility in HCl-ethanol. Each of these five fractions (H1, H3, H4, H2A and H2B, respectively) were characterized by electrophoresis on SDS or Triton-acid-urea gels and by their amino acid compositions as compared with the homologous histones of calf thymus and chicken erythrocytes. This revealed the following: H3 and H4 are strictly analogous to their animal counterparts. However, H4 has an unexplained lower electrophoretic mobility in Triton-containing acid-urea gels. H1 contains three components with lower electrophoretic mobilities than H1 from erythrocytes, contains more alanine than lysine and has a lower ratio of basic to acidic residues. Both H2A and H2B contain at least four variants each, with higher molecular weights than in animals and higher lysine to arginine ratios. H2A variants comigrate in acid-urea-Triton gels with chicken erythrocytes H2A, whereas H2B migrate much slower. It was concluded that the presence of multiple major variants of H2A and H2B is a frequent but not universal feature in cereals. The existence of these variants is not restricted to the embryonic stage as previously suggested for wheat (31).

Journal of Tissue Culture Methods, 1999

Although the basic mechanisms which control the progression through the cell cycle appear to be c... more Although the basic mechanisms which control the progression through the cell cycle appear to be conserved in all higher eukaryotes, the unique features of the plant developmental programme must be somehow reflected in a plant-specific regulation of the factors which control cell division. In the last few years, considerable progress has been achieved in identifying the major components of the cell cycle in plants. The question of how these components direct expression of specific genes at specific stages of the cell cycle, and how they are themselves regulated, constitutes a challenge for the present and the next years. This review summarizes our current knowledge at molecular and biochemical levels of cell cycle-regulated expression in the model system, the synchronized tobacco BY2 cell suspension, and discusses the results in comparison to those obtained by different methods and in other plant systems.