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Biomedical subjects

J Knowland

Publications and source records attributed to J Knowland.

34 records · Page 2Linked to original sources
PubMed1979

Classes of proteins synthesized in oocytes, eggs, embryos, and differentiated tissues of Xenopus laevis.

Two-dimensional gel electrophoresis has been used to analyse protein synthesis in embryonic stages and in three differentiated tissues of Xenopus laevis. The patterns found in oocyte, unfertilized eggs, embryos shortly after fertilization and at progressively later stages of development have been characterized and compared with the patterns found in the brain, heart and liver of tadpoles. The results suggest that at least four classes of proteins can be recognized among the proteins synthesized, although other categories may exist. They also suggest that some proteins synthesized rapidly in the oocyte are likely to be synthesized in differentiated tissues as well, while proteins synthesized for the first time only after fertilization are much less likely to be synthesized in differentiated tissues.

Animals↗
PubMed1979

The activity of cholinesterases during the development of Xenopus laevis.

The activity of cholinesterases during the early development of Xenopus laevis has been examined, and the activity of acetylcholinesterase in particular has been distinguished from other cholinesterases. In contrast to some earlier findings, the activity of acetylcholinesterase is low at early stages and gradually increases during development. Possible reasons for the differences between the earlier results and those reported here are discussed.

Acetylcholinesterase↗
PubMed1978

Induction of vitellogenin synthesis in Xenopus laevis tadpoles.

Oestradiol induces vitellogenin synthesis in vitro in liver taken from Xenopus laevis tadpoles that are in late metamorphosis. Inducibility first appears at the end of prometamorphosis, and the response to oestradiol increases during the completion of metamorphosis. Oestradiol continuously present during development does not influence the stage at which tadpole liver becomes inducible. It seems that the acquisition of inducibility is part of the normal development of the liver, and independent of both the supply of oestrogen and the sex of the tadpole.

Animals↗
PubMed1978

An estrogen receptor from Xenopus laevis liver possibly connected with vitellogenin synthesis.

This paper describes an estrogen receptor which is found in both the nucleus and cytoplasm of liver cells from male Xenopus laevis, and which seems to be involved in the induction of vitellogenin synthesis. It has a high affinity for estradiol (Kd = 0.5 x 10(-9) M), and the affinities of various steroids for the receptor correlate well with their ability to induce vitellogenin synthesis. It sediments at 3.5S at 0 degrees C in 0.5 M KCI. The rate of sedimentation is unaffected by incubation at 20 degrees C prior to centrifugation, but increases if the salt concentration is lowered to 0.1 M KCI or to zero. It has a Stokes radius of 2.6 nm and a molecular weight of approximately 40,000. The receptor is present at very low levels compared to other steroid target tissues (50--100 fold less than chick oviduct). The cytoplasm of a single hepatocyte contains 92 +/- 18 binding sites for estradiol, while each nucleus contains 99 +/- 19 sites.

Animals↗
PubMed1976

Messenger RNA for the coat protein of tobacco mosaic virus.

TMV RNA is not an efficient template for translation of the viral coat protein, in spite of containing nucleotide sequences coding for the protein. Efficient translation requires the prior synthesis within infected cells of a smaller RNA carrying only a portion of the information encoded in the whole genome.

Cell-Free System↗
PubMed1975

Synthesis of vitellogenin in cultures of male and female frog liver regulated by estradiol treatment in vitro.

Using the frog Xenopus laevis, we show that the addition of physiological concentrations of estradiol to cultures of liver from untreated males rapidly induces the synthesis of large amounts of vitellogenin. Sustained synthesis of vitellogenin requires continuous exposure to estradiol. A nonestrogenic steroid, dexamethasone, does not induce vitellogenin synthesis but does induce increased synthesis of a different protein in liver cultures.

Animals↗
PubMed1974

Protein synthesis directed by the RNA from a plant virus in a normal animal cell.

RNA from tobacco mosaic virus can be translated inside oocytes of the frog Xenopus laevis. The main product is a polypeptide with a molecular weight of 140,000. There is no evidence for coat protein synthesis, and it is unlikely that the polypeptide that is made contains either a whole or a partial coat protein sequence. The picture of translation of tobacco mosaic virus RNA obtained using oocytes is very much simpler than that found using cell-free protein-synthesizing systems, in which a great many polypeptides are made under the direction of tobacco mosaic virus RNA. The reasons for this difference are discussed, and the relative merits of in vivo and in vitro protein-synthesizing systems are compared.

Animals↗