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Biomedical subjects

R S Gupta

Publications and source records attributed to R S Gupta.

At least 253 records · Page 14Linked to original sources
PubMed1977

The molecular basis of emetine resistance in Chinese hamster ovary cells: alteration in the 40S ribosomal subunit.

The molecular basis of resistance to the protein synthesis inhibitor emetine has been examined in cell-free, protein-synthesizing extracts derived from normal and emetine-resistant (EmtR) mutants. We had earlier shown that protein synthesis in extracts of the mutant cells was resistant to the inhibitory action of emetin. When extracts from a wild-type and mutant cell line were fractionated into supernatant (S-100) and polyribosome fractions and mixed in different combinations, resistance to emetine was found to be associated with the mutant polyribosome fraction. Further fractionation of wild-type and mutant polyribosomes into 40S and 60S ribosomal subunits and mixing them in various combinations with an S-100 fraction from the wild-type cell indicates that resistance of mutant cells to emetine involves an alteration in the 40S ribosomal subunit. The behavior of EmtR has also been examined in somatic cell hybrids. Studies of EmtR X EmtS hybrid cell lines in vivo and in vitro show that EmtR is pheontypically recessive to EmtS, which is consistent with the ribosomal location of the genetic change.

Cell Line↗
PubMed1977

Purification and properties of dihydrofolate reductase from methotrexate-sensitive and methotrexate-resistant Chinese hamster ovary cells.

We have previously described methotrexate-resistant Chinese hamster ovary cells which appear to contain normal levls of a structurally altered dihydrofolate reductase (EC 1.5.1.3) (Flintoff, W.F., Davidson, S.V., and Siminovitch, L. (1976) Somatic Cell Genet.2,245-261). By selecting for increased resistance form these class I cells, class III resistant cells were isolated which appeared to possess an increased activity of the altered enzyme. In the report, we describe the purification and several properties of the reductase from wild-type cells, two independently selected class I cells, and class III resistant cell. The reductases from wild-type and resistant cells had similar specific activities using folate and dihydrofolate as substrates, and similar molecular weights as determined by sodium dodecyl sulfate gel electrophoresis. The mutant enzymes, however, were about six- to eight-fold more resistant to inhibition by methotrexate than the wild-type enzyme, suggesting a decreased affinity of the mutant reductases to methotrexate-binding. Small differences between various enzymes were also seen in other physicochemical properties such as pH optima and Km values for folate, and in their heat stabilities, which suggest that different structural alterations may lead to the same mutant phenotype. As expected from earlier studies with crude extracts, class III cells did produce a higher (about 10-fold) yield of the reductase than the class I or wild-type cells.

Cell Line↗
PubMed1977

Planning process and machinery in India.

The Constitution of India, with a federal system, having clear division of functions between the Centre and the States, and following the Parliamentary System of Democracy on the British model, makes the task of formulating and carrying out a National Five-Year Plan fundamentally different from any other country of the world. With what process the Five-Year Plan document is prepared and how its objectives and sector plans are approved by the elected representatives of the people and what extra-constitutional means have been adopted to seek the approval of the constituent units of the Union before a Plan is implemented is the theme of this article.

India↗
PubMed1976

The isolation and preliminary characterization of somatic cell mutants resistant to the protein synthesis inhibitor-emetine.

Emetine reversibly inhibits protein synthesis in Chinese hamster ovary (CHO) cells. Stable mutants which are 20-80 fold more resistant to the cytotoxic action of the drug can be isolated in a single step at a frequency of about 2-5 X 10(-7). The frequency of such mutants is increased 30-50 fold by ethyl methane sulphonate mutagenesis, and the spontaneous rate of mutation to emetine resistance as measured by Luria-Delbruck fluctuation analyses is 4.9 X 10(-7) mutations per locus per generation. Protein synthesis in extracts of the mutant cells is resistant to the inhibitory action of the emetine, indicating that the molecular lesion in these cells lies in the protein synthesis machinery.

Cell Line↗
PubMed1976

The isolated cremaster muscle preparation and (external) spermatic nerve-cremaster muscle preparation of the guinea-pig.

The isolated cremaster muscle preparation and spermatic nerve-cremaster muscle preparation of the guinea-pig were studied in vitro to determine their suitability as pharmacological test models. The preparation was contracted by acetylcholine, carbachol, succinylcholine and decamethonium (pD2 values, 4-2, 5-3, 7-3 and 7-4, respectively) through an action on a curare-sensitive cholinoceptor. Lobeline and DMPP were ineffective. Nicotine contracted the muscle, but there was tachyphylaxis. Tubocurarine and hexamethonium presumably competitively antagonized acetylcholine (pA2 values, 7-3 and 5-8); lobeline was a non-competitive antagonist (pD'2 value, 6-4). Atropine and mecamylamine exerted a dualistic action against acetylcholine (final pD'2 values, 5-3 and 6-7, respectively). Tubocurarine, succinylcholine and decamethonium exhibited their typical action when tested with spermatic nerve-cremaster muscle preparation; the latter two drugs also produced muscle spasm. Hexamethonium was a weak blocker of neuromuscular transmission. Atropine, mecamylamine, lobeline and DMPP exhibited neuromuscular blocking activity; however, directly evoked muscle twitches were also notably affected. The cremaster muscle preparations seem to add usefully to the list of currently used in vitro tests, with the added advantage that a mammalian skeletal muscle model is used for simultaneous quantitative studies.

Abdominal Muscles↗
PubMed1976

Coupling of rates of transcription, translation, and messenger ribonucleic acid degradation in streptomycin-dependent mutants of Escherichia coli.

The growth rates of streptomycin-dependent mutants varied in proportion to the level of streptomycin supplied; growth also varied characteristically from one dependent strain to another at a given streptomycin concentration. When cells growing at different rates (over a threefold range) were treated with rifampin, direct proportionality was observed for three parameters: (i) the rates of shutoff of transcription of total ribonucleic acid (RNA) and ribosomal RNA, as measured by pulse labeling at later times; (ii) the translation time for molecules of beta-galactosidase; and (iii) the rate of chemical degradation of messenger RNA. In contrast, the rate of functional inactivation of both total and beta-galactosidase messenger RNA was about the same at all growth rates. None of the variations of growth or other parameters were observed in an otherwise isogenic streptomycin-resistant strain treated with streptomycin. Since the mutational change in strd mutants and the site of action of streptomycin are in the 30S ribosomal subunits, it is suggested that the rate of ribosome function is set by the dependent lesion (and the level of streptomycin). One possibility is that the other correlated effects are mechanistically "coupled" to ribosome function, but the apparent coupling could also be an indirect result of differential effects of streptomycin on variables such as ribosomal miscoding and nucleotide pool size. However, since the rate of functional inactivation of messenger RNA is constant even when the RNA is broken down two- to fourfold more slowly, translation yield tends to be proportional to the growth rate of the dependent strains.

Escherichia coli↗