[Comparison of specific synthesis of RNA in synchronized Euglena gracilis (Z) grown on lactate medium in the dark and in the light, and a study of the mitochondria]

Biosynthesis of ribulose-1.5-bisphosphate carboxylase in greening cells of Euglena gracilis : The accumulation of ribulose-1.5-bisphosphate carboxylase and of its subunits

Light induction of chloroplast development in Euglena leads to quantitative changes in the protein composition of the soluble cell part. One major part of these is the observed accumulation of ribulose-1.5-bisphosphate carboxylase/oxygenase (RuBPCase) enzyme (EC 4.1.1.39). As measured by immunoelectrophoresis, a small amount of RuBPCase (about 10(-6) pmol) is present in a dark-grown cell, whereas a greening cell (72h) contains 10-20 pmol enzyme. Both the cytoplasmic and chloroplastic translation inhibitors, cycloheximide and spectinomycin, have a strong inhibitory effect on the synthesis of the enzyme throughout the greening process of Euglena cells. Electrophoretic and immunological analyses of the soluble phase prepared from etiolated or greening cells do not show the presence of free subunits of the enzyme. For each antibiotic-treated greening cell, the syntheses of both subunits are blocked. Our data indicate that tight reciprocal control between the syntheses of the two classes of subunits occurs in Euglena. In particular, the RuBPCase small subunit synthesis in greening Euglena seems more dependent on the protein synthesis activity of the chloroplast than the syntheses of other stromal proteins from cytoplasmic origin.

[Periodic, metabolic and structural phenomena in a protist, Euglena gracilis]

Sychronous divisions of Euglena gracilis strain Z can be obtained by various methods. When the cells are cultivated in a medium containing lactate as the sole carbon source, synchronous divisions are observed, independent of the conditions of illumination. Nevertheless, there exists a relationship between the phase of cell division and ther periods of light and darkness applied to the culture. During the cell cycle, the synthesis of macromolecules is discontinuous--this is true of nuclear and mitochondrial DNA, ribosomal and nonribosomal RNA, and certain proteins (cytochrome c 558). Cyclic variations in the structure of mitochondria and chloroplasts are observed. In the course of the cell cycle, sequential metabolic processes accompany structural modifications of the organelles. Also, at the beginning of the cycle, at the start of phase G1, the cytoplasmic ribosomes are synthesized, and then, in green euglenids, nonribosomal RNAs are formed. These syntheses of RNA precede enlargement of the chondriome and plastids. In mid-G1 phase, a new synthesis of RNA begins, which precedes synthesis of nuclear and mitochondrial DNA. At the end of G1 phase, division of organelles starts, beginning with the chondriome and plastids, arranged in a network.

[Synthesis of heavy RNA during a cell cycle in Euglena gracilis]

In a previous investigation we had observed discontinuous RNA synthesis during the cell cycle of Euglena gracilis grown synchronously in the light or in the dark. In the present study, we analyse which RNA species are synthesized during the several phases of the cell cycle. During cell division, sedimentation analysis of RNA on sucrose gradients and polyacrylamide-agarose gel electrophoresis show a labeled 30 S RNA peak having a molecular weight of 2.1x10(6) daltons. This type of RNA seems heterogeneous on the basis of its behaviour in polyacrylamide-agarose gel electrophoresis, and is composed of at least two different molecular species. Their synthesis is inhibited by cycloheximide (50 μg/ml). This RNA is degraded preferentially to 13 S material. By autoradiography using a light microscope, we can observe extensive labeling in the nucleolus of dividing cells. Kinetics of labeling, chase experiments, and concomitant synthesis of heavier RNA (40 S and 35 S) tend to identify the 30 S RNA as the immediate precursor of one or both cytoplasmic ribosomal RNA molecules.

[Low temperature spectral study on Euglena gracilis Z during synchronous culture on lactate medium: Variation of cytochrome 556 content]

Low temperature spectra are described for whole Euglena cells. Euglena growing in synchronous culture with lactate medium show a cyclic variation of cytochrome 556 content during each cellular generation. The greatest quantity of cytochrome 556 seems to coincide with the non-dividing phase of the cells, the phase in which the mitochondrial network is observed. On the other hand after treatment of the Euglena with antimycin A, a correlation exists between the formation of giant mitochondria and an increase in the quantity of cytochrome 556.These results demonstrate the existence of a cyclic variation of cytochrome 556 synthesis in Euglena during synchronous growth on lactate medium.