A covalently linked DNA-RNA molecule from human leukemia cells

Suppression of the DnaA phenotype by mutations in the rpoB cistron of ribonucleic acid polymerase in Salmonella typhimurium and Escherichia coli

A class of mutations that confer resistance to rifampin in Salmonella typhimurium and Escherichia coli also suppresses the thermosensitivity of chromosome initiation in dnaA mutants. Ribonucleic acid polymerase is resistant to rifampin in vitro in these suppressive mutants, and the suppressors of dnaA cannot be separated from the rpoB mutations by transduction. It is concluded, therefore, that certain rpoB mutations may suppress the DnaA phenotype.

The involvement of RNA in the initiation of DNA synthesis in mammalian cells. Artifacts arising during caesium-salt density-gradient centrifugation which simulate a covalent attachment of RNA to newly synthesized DNA

Artifacts were encountered during caesium salt density gradient centrifugation which simulated results expected if newly synthesized DNA is covalently attached to RNA. Newly synthesized DNA (in baby hamster kidney cells, BHK-21/C13), pulse-labelled with [3H]thymidine for 10 min at temperatures below 25 degrees C, banded at a greater buoyant density than mature [14C]DNA (heat-denatured nucleic acids) when centrifuged to equilibrium in caesium chloride gradients. Some of the newly synthesized RNA, labelled with [3H]uridine, banded at a buoyant density slightly greater than DNA in caesium sulphate gradients. These results were not obtained when nucleic acids were pulse-labelled at 37 degrees C, nor when samples were heat-denatured in the presence of formaldehyde. This suggests that nucleic acids can aggregate during centrifugation; this is discussed in relation to the molecular size of the DNA.