PubMed Health⌕ Search

Biomedical subjects

R M Hecht

Publications and source records attributed to R M Hecht.

26 records · Page 2Linked to original sources
PubMed1980

A squash technique demonstrating embryonic nuclear cleavage of the nematode Caenorhabditis elegans.

A simple squash technique was developed which permits the observation of individual nuclei during embryogenesis of Caenorhabditis elegans. The technique consists of placing several two-cell stage embryos on a subbed slide in a droplet of M-9 salt buffer and incubating them in a sealed humidity chamber at 16.4 degrees C for increasing time intervals. The embryos are then squashed, fixed, and stained with Hoechst 33258. Rate of cleavage at 25.0 degrees C is 1.8 times faster than that at 16.4 degrees C. This yields superimposable growth curves upon correction for temperature. An initial lag in the rate of nuclear cleavage is followed by a burst of cell proliferation, which continues and then slows before 550-580 cells are produced at 4 to 5 hr at 25 degrees C. The squash size increases with cell number and reaches a maximum at about the 400-cell stage when early morphogenesis begins. The second half of embryogenesis is characterized by histogenesis in which the cells are held more tightly together, individual nuclei become less distinct, and the squash size decreases to a minimum as a small worm is formed.

Animals↗
PubMed1976

Studies of DNA bound RNA molecules isolated from nucleoids of Escherichia coli.

Methods are developed for studying RNA molecules bound directly to DNA in bacterial nucleoids. It is found that among the 1000-3000 nascent RNA chains that normally are attached to the DNA via their associated RNA polymerase molecules, 74 +/- 14 chains per nucleoid can be bound differently. These chains unlike the other nascent RNAs remained bound to the DNA after the chromosome was deproteinized and sheared. Sensitive assays using radioactive labels detected no RNA polymerase involved in the RNA-DNA linkage. The linkage was stable at low temperatures, but the RNA separated from the DNA at high temperature. The bound RNA molecules were heterodisperse (weight average length 1200 bases). Pulse-chase experiments and studies of the fate of these RNA molecules in rifampicin treated cells demonstrated that they are nascent RNAs, degraded or released from the DNA in vivo with kinetics similar to that of the total nascent RNA. Hybridization analyses showed that the chains are composed at least in part of nascent rRNA and known mRNA molecules. Some, but not more than 5% of the bound chains, contained sequences of about 300 nucleotides in length, bound to the DNA in an RNase resistant form.

Binding Sites↗
PubMed1975

Analysis by isopycnic centrifugation of isolated nucleoids of Escherichia coli.

The isolated, formaldehyde-fixed nucleoid of E. coli has been analyzed by isopycnic centrifugation in CsCl density gradients. The membrane-free nucleoid bands at a density of 1.69 +/- 0.02 g/cm3. The membrane-associated nucleoid bands at a density of 1.46 +/- 0.02 g/cm3. Both species sediment to equilibrium as nearly monodisperse bands in CsCl, suggesting that the nucleoid components of DNA, RNA and protein are present in relatively constant ratios. These ratios are constant regardless of the position of the nucleoids in the heterogeneous sedimentation profile of a preparative sucrose gradient. The fixed nucleoids remain condensed during isopycnic centrifugation and there is no detectable loss of RNA from the nucleoid.

Bacterial Proteins↗