Rate Of Net Synthesis Research Articles

The persistent effects of perinatal hypothyroidism on pituitary, thyroidal, and gonadal functions.

Abstract In view of the persistent consequences of neonatal hyperthyroidism, the late effects of brief perinatal hypothyroidism were studied in the rat. The administration of propylthiouracil (PTU) either during the end of pregnancy or neonatally or both resulted in a persistently enlarged thyroid gland associated with an elevated pituitary and hypothalamic thyroid-stimulating hormone (TSH) content, a diminished rate of net synthesis of TSH, and a slightly diminished serum thyroid hormone concentration. Comparable PTU treatment of both young and adult rats failed to produce persistent changes in pituitary TSH content or in the PBI. Perinatal hypothyroidism also caused a delay in puberty with prolongation of estrous cycles. Treatment with thyroxin (T 4 ) neonatally, after prenatal PTU administration, prevented the late pituitary-thyroidal changes but not the gonadal effects. The possibility that pregnant women receiving PTU during pregnancy may have children with mild late gonadal and thyroidal alterations must be considered and should be studied.

Chain growth rate of messenger RNA in Escherichia coli infected with bacteriophage T4

The RNA synthesized in Escherichia coli, infected with T4 bacteriophage at 37 °C, was labeled with radioactive uridine, beginning at three minutes after infection. At various times the cells were lysed by dilution into a 100 °C solution of sodium dodecyl sulfate and salts; this procedure is shown to prevent breakdown of RNA. The cell lysates were centrifuged through sucrose gradients together with E. coli nucleic acids as optical sedimentation markers. From the sedimentation distributions of radioactive RNA the fraction F = radioactivity at a given sedimentation velocity total radioactivity in the distribution was determined at different labeling times. In this way several kinetics of F were obtained, each corresponding to a chosen sedimentation velocity. In these kinetics, F initially increases or remains constant and later decreases; the duration of the initial phase of increase or constancy, respectively, is shown to be equal to the time needed to polymerize RNA molecules sedimenting at the corresponding velocity. Using these synthesis times and converting sedimentation velocity into molecular weight of RNA, the RNA chain growth rate is estimated to be 28 nucleotides/sec. Study of the kinetics of uridine incorporation into RNA of uninfected and T4-infected bacteria and study of the net synthesis of bacterial RNA at different uridine concentrations in the medium gave the following results: (a) the net synthesis rate of bacterial RNA (in uninfected cells) and the RNA chain growth in infected cells are independent of the uridine concentration in the medium; (b) at 0.25 mμmole and at more than 6 mμmoles uridine/ml. in the medium, only 6%, and almost all pyrimidines in RNA, respectively, are derived from the medium.

Genetic regulation of peptide synthesis in hemoglobins.

The structural genes for the chains of hemoglobin control not only the amino acid sequence but also the net rate of synthesis of the chains. In some cases, high rate of destruction associated with a structural abnormality is an important factor in net synthesis. Balanced net production of α and β chains is probably maintained by selection against mutations that result in gross imbalance, since gross imbalance causes hemolytic anemia or death. Minor imbalances may be compensated for by destruction of excess chains without destruction of red blood cells. A proposed model for control of rate of synthesis of the globin chains postulates that completed chains are released from mRNA at a rate determined by the slowest step in their assembly. Decreased synthesis can result from a mutation that results in a slower step anywhere along the mRNA. On the other hand, increased synthesis can only result from a change in the specific position of the rate-limiting step.

Induction of cellular morphogenesis in Myxococcus xanthus. II. Macromolecular synthesis and mechanism of inducer action.

Sadler, William (University of Minnesota, Minneapolis), and Martin Dworkin. Induction of cellular morphogenesis in Myxococcus xanthus. II. Macromolecular synthesis and mechanism of inducer action. J. Bacteriol. 91:1520-1525. 1966.-Net changes in ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and protein syntheses in cells of Myxococcus xanthus during induced, synchronous conversion to microcysts are described. The net synthesis of all three macromolecules was temporarily halted for a brief period during the initiation of shape change. Synthesis then resumed and leveled off when refractile microcysts began to appear. The conversion was completely sensitive, throughout the process, to low concentrations of chloramphenicol and actinomycin D. The uptake of amino acids and uracil was linear throughout the conversion, suggesting that the plateaus in rates of net synthesis of protein and RNA represented a period of rapid turnover. The most effective inducers of microcyst formation were fully saturated aliphatic compounds containing 2 to 4 carbon atoms and at least one primary or secondary alcohol group. Studies with labeled inducer indicated that the inducer need not be taken up by the cells to be effective, and probably interacts with some peripheral structure of the cell. The possibility that induction involves an alteration of a membrane-DNA complex is discussed.

Stability of deoxypentosenucleic acid in growing and non-growing livers of young rats

Weaning rats of the same litter, which had been administered 32P through the milk of mother rats, were used. The total quantity and total radioactivity per liver of DNA-P and PNA-P were determined along with the specific activity of acid-soluble P of the same organ at an interval of some 10 days, during which period the growth rate of the animals was changed by controlling the food intake. Using these data the fractional rates of breakdown (= rates of renewal in most cases) of DNA and PNA of the liver were calculated using a formula obtained by solving Branson's integral equation on some appropriate assumptions. The rates of DNA breakdown in the region of zero showed no trend on increase or decrease with the increase in the rate of net synthesis of DNA, while the rates of PNA breakdown proved to be of considerable magnitude. Thus there is no evidence of such an extreme labilisation of DNA-P during mitosis of the cell as was implied by the hypothesis of the Leblond school. The DNA rather seems to be metabolically inert whether it is being actively synthesised or not.