Polyribonucleotide synthesis by subfractions of microsomes from rat liver

1. The microsome fraction of rat liver has been fractionated and the ability of the fractions to incorporate ribonucleotides into polyribonucleotides has been studied. Activity was found in the rough-surfaced vesicle (light) fraction and in the free-ribosome fraction and this latter activity has been examined. 2. The free-ribosome fraction contains ribosome monomers, dimers and trimers together with some higher oligomers and ferritin. In addition to catalysing the incorporation of ribonucleotides into acid-insoluble material it contains diesterase activity. It catalyses the incorporation of UMP from UTP, but not UDP, AMP from ATP and CMP from CTP into polyribonucleotide material, and for UTP the product appears to be a homopolymer not more than eight units long attached to the ends of primer polyribonucleotide strands. 3. The activity could not be removed from the free-ribosome fraction by washing or by isolation in the presence of ethylenediaminetetra-acetic acid. 4. Partially hydrolysed polyuridylic acid but not polyadenylic acid could serve as a primer for the incorporation of UMP, but some activity was always associated with an endogenous primer. 5. Analysis of RNA extracted from the free-ribosome fraction after incubation with [3H]UTP showed the presence of 28s, 18s, 5s and transfer RNA types, but no radioactivity was associated with any of these RNA fractions.

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Nuclease activity in cell-free amino acid-incorporating systems from chicken liver

Biochemical Journal ◽

10.1042/bj1090185 ◽

1968 ◽

Vol 109 (2) ◽

pp. 185-190 ◽

Cited By ~ 24

Author(s):

Jack G. Siler ◽

Melvin Fried

Keyword(s):

Amino Acid ◽

Rat Liver ◽

Liver Cell ◽

Free Amino ◽

Nuclease Activity ◽

Chicken Liver ◽

Lower Activity ◽

Insoluble Material ◽

Polyuridylic Acid ◽

System 2

1. Comparative studies of the polyuridylic acid-directed phenylalanine-incorporating activity of cell-free systems derived from rat and chicken livers demonstrated markedly lower activity in the chicken liver system. 2. The chicken liver cell sap contained the factor(s) responsible for this lower activity. Ribosomes from chicken and rat performed equally well in the presence of rat liver cell sap. Chicken liver cell sap, when mixed with rat liver cell sap, caused an inhibition of incorporation of phenylalanine into acid-insoluble material. 3. Though ribosomal preparations and cell sap from both rat and chicken liver degraded polyuridylic acid to some extent, the chicken liver cell sap contained the largest amount of activity. 4. Rat liver cell sap inhibited the nuclease activities of ribosomal preparations, but no such nuclease inhibition could be demonstrated with chicken liver cell sap.

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A Quantitative Analysis of Proflavine Binding to Polyadenylic Acid, Polyuridylic Acid, and Transfer RNA

European Journal of Biochemistry ◽

10.1111/j.1432-1033.1971.tb01595.x ◽

1971 ◽

Vol 23 (1) ◽

pp. 86-95 ◽

Cited By ~ 76

Author(s):

Maurice Dourlent ◽

Claude Helene

Keyword(s):

Quantitative Analysis ◽

Transfer Rna ◽

Polyadenylic Acid ◽

Polyuridylic Acid

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Chain extension of ribonucleic acid by enzymes from rat liver cytoplasm

Biochemical Journal ◽

10.1042/bj1090485 ◽

1968 ◽

Vol 109 (4) ◽

pp. 485-494 ◽

Cited By ~ 24

Author(s):

N. M. Wilkie ◽

R. M. S. Smellie

Keyword(s):

Rat Liver ◽

Alkaline Hydrolysis ◽

Actinomycin D ◽

Chain Extension ◽

Supernatant Fraction ◽

Inorganic Pyrophosphate ◽

Optimum Ph ◽

Microsome Fraction ◽

Hydrolysis Of ◽

Generating System

1. The 105000g supernatant fraction of rat liver catalyses the incorporation of ribonucleotides from ribonucleoside triphosphates into polyribonucleotide material. The reaction requires Mg2+ ions and is enhanced by the addition of an ATP-generating system and RNA, ATP, UTP and CTP but not GTP are utilized in this reaction. In the case of UTP, the product is predominantly a homopolymer containing 2–3 uridine residues, and there is evidence that these may be added to the 3′-hydroxyl ends of RNA or oligoribonucleotide primers. 2. The microsome fraction of rat liver incorporates ribonucleotides from ATP, GTP, CTP and UTP into polyribonucleotide material. This reaction requires Mg2+ ions and is enhanced slightly by the addition of an ATP-generating system, and by RNA but not DNA. Supplementation of the reaction mixture with the three complementary ribonucleoside 5′-triphosphates greatly increases the utilization of a single labelled ribonucleoside 5′-triphosphate. The optimum pH is in the range 7·0–8·5, and the reaction is strongly inhibited by inorganic pyrophosphate and to a much smaller degree by inorganic orthophosphate. It is not inhibited by actinomycin D or by deoxyribonuclease. In experiments with [32P]UTP in the absence of ATP, GTP and CTP, 80–90% of 32P was recovered in UMP-2′ or −3′ after alkaline hydrolysis of the reaction product. When the reaction mixture was supplemented with ATP, GTP and CTP, however, about 40% of the 32P was recovered in nucleotides other than UMP-2′ or −3′. Although the reactions seem to lead predominantly to the synthesis of homopolymers, the possibility of some formation of some heteropolymer is not completely excluded.

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Contamination of free-ribosome fractions by detached previously membrane-bound ribosomes (Short Communication)

Biochemical Journal ◽

10.1042/bj1380305 ◽

1974 ◽

Vol 138 (2) ◽

pp. 305-307 ◽

Cited By ~ 4

Author(s):

K. O'Toole

Keyword(s):

Rat Liver ◽

Membrane Fraction ◽

Short Communication ◽

Free Ribosome ◽

Membrane Bound ◽

Free Polyribosome

A rough-membrane fraction isolated from rat liver by a procedure designed to prevent membrane denaturation was subjected to the gradient treatment normally used to isolate free ribosomes. Under these conditions, at most 20% of the ribosomes were detached from membrane with less than 5% sedimenting into the free-polyribosome pellet.

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