Adenosine 3',5'-monophosphate: regional differences in chick embryos at the head process stage

The concentrations of adenosine 3',5'-monophosphate and adenosine triphosphate and the activity of phosphodiesterase were determined in different regions of chick embryos at the head process stage. Adenosine 3',5'-monophosphate, adenosine triphosphate, and phosphodiesterase were estimated to be higher in the mesoderm-forming portions of the hypoblast than in portions that form neural structures from Hensen's node or the epiblast.

Comparison of the transfer RNA complements of chick embryos and their supporting membranes

The transfer RNA complement of 5- to 6-day chick embryos was compared with that of the associated membranes by chromatography of preparations of aminoacyl-tRNAs on columns of benzoylated diethyl-aminoethylcellulose. Profiles of all aminoacyl-tRNAs were determined under conditions selected for emphasis on the region containing a component believed to play a role in regulating onset of rapid hemoglobin synthesis in the blood islands of young blastodiscs. Differences in profile were observed only for alanyl- and glutamyl-tRNAs. A marked quantitative change in the distribution of components in the complement of glutamyl-tRNAs was in the converse direction of that required for increase in content of putative regulator and was not further investigated.Small reproducible differences in the profiles of alanyl-tRNAs were further investigated and were shown to be due to a marked increase in the content of a distinct minor component of the alanyl-tRNA complement of the membranes relative to that of the embryo.

DNA polymerase of chicken embryo: purification and properties

The almost complete purification of the previously reported DNA polymerase of chicken embryo is described; in the final isolation step the enrichment of the enzyme, which comprises about 0.01% of the protein extractable from 10-day-old embryos, is more than 9000-fold. The enzyme is a basic protein (pI = 9.15), of molecular weight about 27,000. It exhibits no nuclease activity, requires Mn(2+) ion for activity, and may contain Zn. It is very sensitive to oxidation.

Endogenous RNA-directed DNA polymerase activity in uninfected chicken embryos

Early chicken embryos that are either positive or negative for group-specific antigens of avian leukosis viruses contained endogenous RNA-directed DNA polymerase activity. This endogenous DNA polymerase activity was not increased after mixture of soluble DNA polymerases isolated from chicken embryos with disrupted chicken embryo cells. The endogenous activity was resistant to treatment with deoxyribonuclease, and the initial rate of DNA synthesis was partially resistant to actinomycin D. In contrast, over 90% of the endogenous polymerase activity was destroyed by ribonuclease in medium with high salt concentration. The DNA product of the endogenous DNA polymerase activity from chicken embryos did not hybridize with RNA of Rous sarcoma virus or reticuloendotheliosis virus, whereas about 40% of this DNA product hybridized with the RNA from the same chicken-cell fraction. Antibody against DNA polymerase of avian myeloblastosis virus did not neutralize the chicken endogenous DNA polymerase activity. These results demonstrate that uninfected chicken embryo cells contain endogenous RNA-directed DNA polymerase activity that is not derived from avian leukosis or reticuloendotheliosis viruses.