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Biomedical subjects

M D Enger

Publications and source records attributed to M D Enger.

At least 55 records · Page 3Linked to original sources
PubMed1979

Cadmium-induced alterations in RNA metabolism in cultures of Chinese hamster cells sensitive to and resistant to the cytotoxic effects of cadmium.

A variant population (CdR) of cultured Chinese hamster cells (line CHO) was derived that is more than 100 times as resistant to the cytotoxic effects of Cd2+ than is the parent population. The effects on RNA metabolism of exposure to sublethal concentrations of Cd2+ were studied in CHO and CdR. Exposure to 2 X 10(-7) M CdCl2 for 24 h resulted in increased polysome content (1.2 times) and increased uridine or adenosine incorporation into heterogeneous nuclear RNA (1.2-1.4 times) and messenger RNA ((1.5-1.7 times) in both populations. Measurement of ATP pool specific activity following exposure to radiolabeled adenosine showed that increased incorporation reflects increased synthesis. The equivalence of CHO and CdR in dose-response in terms of stimulated RNA synthesis and their disparity in dose-response in terms of cytotoxic effects indicate that the systems involved in conferring protection against the lethal effects of Cd2+ are not similarly involved in attenuating the effects on RNA metabolism.

Adenosine↗
PubMed1978

Informosomal and polysomal messenger RNA. Differential kinetics of polyadenylation and nucleocytoplasmic transport in Chinese hamster ovary cells.

The relative kinetics of cytoplasmic appearance and polyadenylation were determined for informosomal (ribosome-free) and polysomal (ribosome-associated) mRNAs of cultured Chinese hamster cells. Label appeared in polysomal mRNA 17--20 min and into informosomal mRNA 2--5 min after addition of radio-labelled uridine. Adenosine appeared in polysomal mRNA 4--5 min before uridine. In contrast, adenosine label preceded uridine into informosomal mRNA by less than 1 min. About one-third of newly formed informosomal and two-thirds of newly formed polysomal mRNA are poly(A+). The data indicate that newly formed informosomal mRNA cannot be simple precursor to polysomal mRNA. Further, the pronounced difference in time required for polyadenylation and cytoplasmic appearances of these messenger ribonucleoproteins suggests that there may be fundamental differences in their mode of processing.

Adenine↗
PubMed1978

Altered aminoacyl-tRNA synthetase complexes in G1-arrested Chinese hamster ovary cells.

Aminoacyl-tRNA SYNTHETASE COMPLEXES EXISTING IN Chinese hamster ovary (CHO) cells were shown to undergo alterations as a function of the growth state of the cell. The distribution pattern for 13 particulate postribosomal aminoacyl-tRNA synthetases in 10-30% (w/v) exponential sucrose gradients was determined for the enzymes from CHO cells as they exist under three different culture conditions: exponential growth, G1 arrest induced by isoleucine deficiency, and G1 arrest induced by leucine deficiency. The synthetases specific for the amino acids Arg, Asp, Cys, Gln, His, Lys, Met, Thr, and Val have indistinguishable distribution patterns in all three cell types. However, the synthetases specific for Glu, Pro, Leu, and Ile have a unique distribution of synthetase forms in the G1-arrested cultures and this distribution is independent of whether G1 arrest was induced by isoleucine or leucine deficiency. The distribution of synthetase forms in G1-arrested cells differs in a definite, reproducible manner from the profiles obtained with the exponentially growing cells, and this fact is strong evidence for an in vivo role for the synthetase complexes.

Amino Acyl-tRNA Synthetases↗
PubMed1976

Effects of ionizing radiation of RNA metabolism in cultured mammalian cells. III. Specific reduction in mRNA synthesis during resumed division and plateau phases following exposure to 800 rads of x irradiation.

The cell growth response of cultured Chinese hamster ovary cells, line CHO, to 800 rads of X irradiation involves a period of division delay, followed by a period of resumed division which terminates in a plateau phase. Over 95% of the cells die eventually. No direct effects of RNA or protein metabolism are evident during the delay period. During the resumed division and beginning of plateau phases, however, a specific and relatively constant reduction in mRNA synthesis relative to messenger-like RNA and heterogenous nuclear RNA synthesis is evidenced. The ratio of mRNA to messenger-like RNA synthesis ranges from 0.8 to 0.65 during these phases. The effect is not due to altered cell-cycle distribution, and evidence is presented to indicate that it is probably not a compensatory response to the unbalanced growth that occurs during the division delay period.

Adenosine↗
PubMed1975

RNA synthesis in Chinese hamster cells. III. Non-coordinate increases during interphase in synthesis rates for informosomal, polysomal and heterogeneous nuclear RNAs.

Cultured Chinese hamster ovary cells were synchronized by mitotic selection. Relative synthesis rates for informosomal messenger-like RNA (mlRNA), polysomal messenger RNA (mRNA), and heterogeneous nuclear RNA (HnRNA) were estimated from the amount of labeled adenosine or uridine incorporated into these species in early and late interphase. The amounts of uridine incorporated into HnRNA, mRNA, and mlRNA during a pulse administered 9.75-10.75 h post-mitosis were 3.48 4.64, and 2.82 times the amounts incorporated 1.5-2.5 h post-mitosis. Adenosine incorporation values 9.5-11.0 h post-mitosis were 1.64 (HnRNA), 2.49 (mRNA), and 1.18 (mlRNA) times the 1.5-3.0 h values. The realitive incorporation into MRNA of large polysomes corresponded to incorporation into mRNA of smell polysomes. Thus, the synthesis rates of mRNA, mlRNA, and HnRNA increase during interphase in a noncoordinate fashion.

Adenosine↗
PubMed1974

The isolation from ribonucleic acid of substituted uridines containing alpha-aminobutyrate moieties derived from methionine.

The RNA of an established line of Chinese hamster cells growing in cell culture contains a small number of uridines substituted at the 3-position with a gamma-linked alpha-aminobutyrate residue. Structure has been ascertained by: (a) examination of incorporation of isotopic labels from precursors; (b) degradation with anhydrous hydrazine and comparison of the products with synthetic material or with hydrazinolysis products of known uridines; and (c) comparison of the unknowns as their hydantoin derivatives with the 5-beta-(bromoethyl)hydantoin alkylation products of uridine and of 1- and 3-methylpseudouridine. In this manner it is shown that 18-S RNA of ribosomes contains a single residue of a nucleoside which we tentatively identify as 1-methyl-3-gamma-(alpha-amino-alpha-carboxypropyl)pseudouridine per molecule. RNA isolated from the supernatant fraction, sedimenting at 4 S and co-electrophoresing with transfer RNA on polyacrylamide gels, contains several similar bases, one of which is identified as 3-gamma-(alpha-amino-alpha-carboxypropyl)uridine. Each of the above nucleosides derives its alpha-aminobutyrate residue from methionine.

Aminobutyrates↗
PubMed1974

Polyribosomal and particulate distribution of lysyl- and phenylalanyl-transfer ribonucleic acid synthetases.

1. Only two aminoacyl-tRNA synthetases from Chinese hamster ovary cells are found associated with ribosomes and polyribosomes. 2. Phenylalanyl-tRNA synthetase activity is found with the 60S subunit, 80S monoribosome and individual polyribosomes. An additional 15S form of the enzyme is also seen. 3. Lysyl-tRNA synthetase activity is found in a form of about 20S and associated with ribosomal subunits and polyribosomes. The ribosomal subunits having lysyl-tRNA synthetase activity are about 6S larger than the bulk of the ribosomal subunits. 4. The lysyl- and phenylalanyl-tRNA synthetases found in different complexes have differential sensitivity to EDTA and centrifugation properties.

Amino Acids↗