Nucleolar and nuclear RNA synthesis during the cell life cycle in monkey and pig kidney cells in vitro.

The incorporation of 5-(3)H-uridine and 5-(3)H-cytidine into nucleolar and nonnucleolar RNA in the nucleus of monkey and pig kidney cells was measured in vitro during the cell life cycle. Time-lapse cinematographic records were made of cells during asynchronous exponential proliferation, in order to identify the temporal position of individual cells in relation to the preceding mitosis. Immediately following cinematography, cells were labeled with uridine-(3)H and cytidine-(3)H for a short period, fixed, and analyzed by radioautography.

TETRACYCLINE FLUORESCENCE IN PERMEABILITY STUDIES OF MEMBRANES AROUND INTRACELLULAR PARASITES.

Certain protozoa, bacteria, and viruses when phagocytosed by host cells become surrounded by an intracytoplasmic boundary. This membrane prevents the fluorescent antibiotic tetracycline from entering the parasites when it is added to the medium, since they show no fluorescence, whereas extracellular parasites are immediately visible. As soon as the host cell dies, the intracellular parasites also become visible.

Selective localization of tetracycline in mitochondria of living cells.

The property of tetracycline to induce fluorescence has been used to determine its localization in living cells. It was found that this antibiotic, as well as the related antibiotics oxytetracycline and chlorotetracycline, specifically combines with the mitochondria of living cells, either in tissue culture or in fresh preparations from various organs.