An improved method has been developed for the preparation of autoradiographs for electron optical study. The refinement lies principally in the routine production of uniformly thin layers of photographic emulsion over the tracer-labeled cell sections. This is accomplished by means of a centrifugal spreading mechanism. Maize root tips grown in the presence of H3-thymidine were examined electron ...

F R O M the results of experiments involving autoradiography of stretched H3 thymidine-labelled salivary gland chromosomes of Drosophila melanogaster, and a consideration of previously published evidence, STEFFENSEN (1963) has concluded that DNA (deoxyribonucleic acid) is absent from the interband regions of these chromosomes. In opposition to this conclusion are the results presented in this r...

To gain further information on the mechanisms by which the fluorinated pyrimidines and their nucleosides inhibit various processes of nucleic acid biosynthesis, studies similar to those re ported in the preceding paper (6) were carried out in vitro in glycolyzing suspensions of the Ehrlich ascites cells system used by LePage for studies of purine biosynthesis (20). In this work the following la...

An improved method has been developed for the preparation of autoradiographs for electron optical study. The refinement lies principally in the routine production of uniformly thin layers of photographic emulsion over the tracer-labeled cell sections. This is accomplished by means of a centrifugal spreading mechanism. Maize root tips grown in the presence of H3-thymidine were examined electron ...

We studied the expression of 11 cell cycle-dependent genes in senescent WI-38 fibroblasts and compared the results to those obtained in WI-38 cells from early passages (young cells). Every gene we examined is expressed in the senescent cells at levels similar to those in the young cells, including two genes maximally expressed at the G1/S phase boundary--genes for thymidine kinase and histone H...

The H3'-C3'-C4'-H4' torsional angles of two microcrystalline 2'-deoxynucleosides, thymidine and 2'-deoxycytidine.HCl, doubly (13)C-labeled at the C3' and C4' positions of the sugar ring, have been measured by solid-state magic-angle-spinning nuclear magnetic resonance (NMR). A double-quantum heteronuclear local field experiment with frequency-switched Lee-Goldberg homonuclear decoupling was use...

The enzymes of the DNA synthesizing machinery constitute a group of gene products that are generally expressed co-ordinately at the G1/S boundary of the cell cycle. We have investigated how growth factors regulate the steady-state mRNA levels of two of these genes, the PCNA (proliferating cell nuclear antigen)/cyclin and the thymidine kinase genes. To detect the PCNA/cyclin mRNA, we isolated a ...

Autoradiographic studies of the effects of some antibiotics, amino acid analogs, and nucleases on the synthesis of DNA have been carried out to gain information on the regulatory mechanism of DNA replication within the cell. Cultured cells of the Chinese hamster and human cancer (HeLa) were used as experimental material. Puromycin, chloramphenicol, p-fluoro-phenylalanine, and methylated tryptop...