Nucleotide polymerases in the developing avian erythrocyte

DNA polymerases of rabbit mammary gland: partial purification, characterization and changes in DNA polymerase activities as a function of physiological state

DNA polymerases alpha and beta were partially purified from rabbit mammary gland, and their properties were examined. Many of these properties (sedimentation coefficients, pH optima, divalent cation requirements, sensitivity to various inhibitors) are similar to those commonly regarded as typical of eukaryotic DNA polymerases alpha and beta. Effect of stage of pregnancy and lactation on the levels of activity of DNA polymerases alpha, beta and gamma in rabbit mammary gland was examined. These experiments reveal a considerable variation of DNA polymerase-alpha activity; the highest enzyme activity is observed on day-20 of pregnancy and on day-1 of lactation.

Modulation of nonglobin mRNA levels in erythropoiesis

During erythropoiesis, the decrease of complexity of a RNA population is an important process as is globin mRNA accumulation. To determine the sequential control process of gene expression, many genomic clones which express in mouse reticulocytes were obtained and used for the titration of each mRNA level in the different stages of erythroid cells. The level of mRNAs of rt-clones decreases depending on the maturation of erythroid cells, and the coordinated and sequential control of this level is likely to be one of the factors affecting this process.

Changes in DNA polymerases alpha, beta and gamma in mouse liver as a function of age

The activities of DNA polymerases alpha, beta and gamma were determined in mouse liver as a function of age by a combination of glycerol density gradient centrifugation with polymerase specific assays. Although alpha polymerase was preserved throughout the life span, the activity dropped sharply from a high level at the fetal and neonatal stages to a level one order lower after maturation through adjustment of the amount of protein administered. beta polymerase showed similar but less drastic changes than alpha. DNA polymerase gamma activity increased about two-fold in going from newborn to adult stages and remained constant after maturation. According to the amount of DNA, DNA polymerase alpha decreased after birth, but the change was less drastic compared to that through adjustment of the amount of protein. DNA polymerase beta increased the activity 2-3-fold within a period of 3 months following birth. gamma polymerase underwent more than a 10-fold increase in activity through adjustment of the amount of DNA within the same period.

Complementation with an avian influenza virus is required for synthesis of M protein of a human strain in chicken erythocytes

The M protein of avian, but not human, strains of influenza A viruses is synthesized in infected chicken erythrocytes. In dual infections an avian strain complemented the human virus and both the human and avian M proteins were expressed.

Primer specificity of ribosome-associated poly(A) polymerase from Ehrlich ascites tumour cells

The reaction product of the ribosomal poly(A) polymerase [ATP(UTP):RNA nucleotidyltransferase] is analyzed. Two systems are used in vitro: (a) isolated polyribosomes with endogenous enzyme and RNA primer and (b) purified enzyme with total polyribosomal RNA as primer. In the polyribosome system about 50% of the [3H]AMP label is in poly(A)-containing mRNA. This RNA displays a heterogeneous size ditribution in the range of 8--30 S with a maximum at about 14 S. Upon denaturation the maximum is shifted towards the 10-S zone. The poly(A) polymerase catalyzes the addition of 12--18 adenylate residues to pre-existing mRNA poly(A) sequences of 40--160 residues. The [3H]AMP incorporated into poly(A)-lacking RNA is mainly in a fraction with an electrophoretic mobility corresponding to 4-S RNA. In the purified enzyme system, specificity towards poly(A)-containing mRNA is lost to a considerable extent. Only 10% of the [3H]AMP label is retained by oligo(dT)-cellulose. The bulk of the product is in 18-S rRNA and heterogeneous small molecular weight RNA. We conclude that the ribosome-associated poly(A) polymerase is most likely the enzyme responsible for the cytoplasmic polyadenylation of poly(A)-containing mRNA in vivo.

Two distinct poly(A) polymerases isolated from the cytoplasm of Ehrlich ascites tumour cells

The poly(A) polymerases from the cytosol and ribosomal fractions of Ehrlich ascites tumour cells are isolated and partially purified by DEAE-cellulose and phosphocellulose column chromatography. Two distinct enzymes are identified: (a) a cytosol Mn2+-dependent poly(A) polymerase (ATP:RNA adenylyltransferase) and (b) a ribosome-associated enzyme defined tentatively as ATP(UTP): RNA nucleotidyltransferase. The cytosol poly(A) polymerase is strictly Mn2+-dependent (optimum at 1 mM Mn2+) and uses only ATP as substrate, poly(A) is a better primer than ribosomal RNA. The purified enzyme is free of poly(A) hydrolase activity, but degradation of [3H]poly(A) takes place in the presence of inorganic pyrophosphate. Most likely this enzyme is of nuclear origin. The ribosomal enzyme is associated with the ribosomes but it is found also in free state in the cytosol. The purified enzyme uses both ATP and UTP as substrates. The substrate specificity varies depending on ionic conditions: the optimal enzyme activity with ATP as substrate is at 1 mM Mn2+, while that with UTP as substrate is at 10--20 mM Mg2+. The enzymes uses both ribosomal RNA and poly(A) [but not poly(U)] as primers. The purified enzyme is free of poly(A) hydrolase activity.

RNA synthesis and RNA polymerase activities in germ cells of developing rainbow trout testis

Spermatogenesis is a complex developmental process which sequentially generates several different germ cell types. These cell types from rainbow trout (Salmo gairdnerii) testis were separated by sedimentation in serum albumin gradients and characterized on the basis of their physical properties, chronological appearance, and protein synthesis. The rate of RNA synthesis, the types of RNA made, and the RNA polymerase activities present were determined for each cell type. The rate of RNA synthesis decreased from a high level in spermatogonia and spermatocytes to a low level in early spermatids and was absent in late spermatids and mature spermatozoa. Newly synthesized RNA in spermatogonia and spermatocytes consisted of a variety of molecular weight species, including 18 S and 28 S ribosomal RNAs. The synthesis of high molecular weight RNAs, especially ribosomal RNAs, decreased drastically in early spermatids, leading to the synthesis of only small molecular weight RNAs. RNA polymerase I and II were present in all cell types but the activities of both showed large decreases between spermatocytes and middle spermatids. Both RNA polymerase activities were almost absent from spermatozoa. The activities of RNA polymerase I and II from unfractionated testis cells at different stages of hormone-induced spermatogenesis were quantitated by fractionation of the solubilized extract on DEAE-cellulose. Both polymerases showed major decreases in activity which began near the chronological mid-point of development. For polymerase I the decrease in activity was over 400 fold, for polymerase II over 200 fold. The number of RNA polymerase II molecules per testis cell, quantitated by the binding of [3H]amanitin to cell extracts, also decreased markedly during spermatogenesis. The reduction in polymerase II activity was accompanied by a parallel 200-fold decrease in[3H]amanitin binding. The reduction in polymerase activity appears, therefore, to be due to an actual reduction in the cellular content of RNA polymerase II molecules. These results suggest that transcription in maturing testes is regulated, at least in part, by the concentrations of the RNA polymerases.

Template specificity of DNA-dependent RNA polymerase from calf liver nuclei

The efficiency of transcription of both mammalian and bacterial templates by 3 distinct multiple forms of DNA-dependent RNA polymerase from calf liver nuclei has been determined. The homologous template and salmon sperm DNA were more efficiently transcribed than bacterial templates. The native DNA/denatured DNA activity ratio of the 2 alpha-amanitin-insensitive forms was found consistent with that described for enzymes exhibiting nucleolar localization.