Einbau von Uridin und Orotsäure in plastidäre ribosomale RNA von Chlorella nach Antibiotica-Behandlung

Zusammenfassung Chlorella pyrenoidosa inkorporiert unter normalen Anzuchtbedingungen kurzfristig angebotenes Uridin fast ausschließlich in plastidäre ribosomale RNA. Es lassen sich rasch markierte Ribosomen und deren Untereinheiten von 70 S, 50 S und 30 S nachweisen. Diese Markierung wird durch Rifampin in geringen Konzentrationen bereits nach wenigen Minuten unterbunden. Auf das Zellwachstum hat Rifampin bei heterotropher Anzucht dagegen auch in höheren Konzentrationen keinen Einfluß. Chloramphenicol hemmt den kurzfristigen Uridin-Einbau in ribosomale Partikeln von 70 S, 50 S und 30 S, nur geringfügig dagegen denjenigen in ribosomale RNA. Auch die Wirkung des Chloramphenicols tritt rasch ein. Cycloheximid beeinflußt den Kurzzeit-Einbau von Uridin in ribosomale Partikeln und in RNA nicht, wenn die Inkubationszeit 60 min nicht überschreitet.Die Markierung der Nucleinsäuren von Chlorella mit 6-(14C)-Orotsäure zeigt vergleichbare Empfindlichkeiten gegen die drei Antibiotica wie der Einbau von 6-(14C)-Uridin und 5-(3H)-Uridin.

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Incorporation of uridine and of orotate into chloroplast ribosome RNA of Chlorella after treatment with antibiotics

Summary Normal grown cells of Chlorella pyrenoidosa incorporate uridine exclusively into chloroplast ribosomal RNA after short time labeling. With sucrose gradient separation, labeled ribosomal particles of 70 S, 50 S and 30 S can be shown. This labeling is prevented by rifampin in low concentrations after a few minutes. At the same concentration of the antibiotic and also with 10-fold higher concentration, no effect on heterotrophic cell growth is observed. This indicates clearly that mitochondria cannot be influenced by rifampin. Chloramphenicol also inhibits the formation of uridine labeled ribosomal particles of 70 S, 50 S and 30 S. In the presence of this antibiotic, some labeled ribosomal RNA is formed. Also the effect of chloramphenicol can be shown after short incubation periods. Cycloheximide treatment of the cells within 30 and 60 min and up to the 10-fold concentration of protein synthesis inhibition (Morris, 1967) results in no effect on labeling of ribosomal RNA and of ribosomal particles in Chlorella with uridine. Only after prolonged treatment of the cells with cycloheximide is some effect on uridine incorporation observed.The comparison of the incorporation patterns of 6-(14C)-orotate, (6-14C)-uridine and 5-(3H)-uridine into nucleic acids in the presence of rifampin, chloramphenicol and cycloheximide shows some similarities. After 60 min incubation with the precursors, the incorporation is reduced by all three antibiotics. In rifampin treated cells, orotate and both uridines are preferentially incorporated into DNA. With chloramphenicol, the relative incorporation of orotate and of uridine into the 5 S and the 16 S RNA is higher as compared with the 23 S RNA. Cycloheximide results in an increase in the relative incorporation of orotate as well of uridine into DNA. The similarities of the effects of the three antibotics indicate that the preferential incorporation of uridine into chloroplast ribosomes of Chlorella is not due to a compartmentation of the uridine-UMP-pathway.

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Abkürzungen BisMSB bis(O-Methylstyryl)-Benzol - PPO 2,5-Diphenyloxazol - MAK-Säule Säule aus methyliertem Albumin mit Kieselgur     

Development of chloroplast membranes during light induced greening ofChlorella fusca g-2

Summary The development of thylakoid protein complexes during light induced greening of a mutant ofChlorella fusca was studied. Separation of chlorophyll-protein complexes and thylakoid polypeptides by LDS-polyacrylamide gel electrophoresis show that cells grown in the dark contain proteins belonging to coupling factor and cytochrome f/b₆ complex. Parts of both reaction centers are present also. The antennae complexes are specifically lost in yellow cells. The changes in polypeptide pattern at different stages of development in the light are related to ultrastructural changes. The beginning of membrane appression can be correlated with the appearance of the light-harvesting complex II. While the average diameter of EF-particles increases throughout the greening process, their densitiesapart from the rearrangement due to membrane stacking-remain fairly constant. The kinetics of EF_u-particle enlargement are different from those of EF_s-particles.PF-faces in thylakoids grown in the dark contain particles of uniform diameter but some of them protrude more from the fracture plane than do their neighbors. During the first hours of greening, their density increases and two classes develop. From the beginning of membrane stacking, the composition of PF_u-faces remains constant and PF_s-particles increase in number for some time.Results are discussed on the basis of present knowledge of structurefunction relations in thylakoids.Abbreviations CF _o intrinsic membrane complex of the coupling factor - EF, EF _s ,EF _u exoplasmic fracture face, stacked and unstacked region, respectively - LDS lithium dodecyl sulfate - LHCII light-harvesting complex of Photosystem II - PF, PF _s ,PF _u protoplasmic fracture face, stacked and unstacked region, respectively - PS I andPS II Photosystem I and Photosystem II