Nature of transient inhibition of deoxyribonucleic acid synthesis in HeLa cells by parainfluenza virus 1 (Sendai)

Adsorption of ultraviolet-inactivated Sendai virus, at high or low multiplicity, to HeLa cells caused a transient increased incorporation of (3)H-thymidine into the cellular deoxyribonucleic acid (DNA). In HeLa cells synchronized by a double-thymidine block, this increased incorporation of thymidine during the S phase lasted from about 30 to 90 min after virus adsorption. The observations that the kinetics of accumulation of radioactive thymidine in the nucleotide pool did not differ in control and in the virus-treated cells and that the (32)P incorporation into the DNA of the virus-treated cells was inhibited at the same time indicate that the augmented incorporation of (3)H-thymidine into DNA results from a transient block in the endogenous pathway of thymidine synthesis. Chromatographic analysis of the nucleotide pool of the virus-treated cells labeled with (14)C-formate indicates that methylation of deoxyuridine monophosphate to thymidine monophosphate is inhibited. It is suggested that the inhibition is caused by a block of either the thymidilate synthetase or some step in the tetrahydrofolate cycle.

Automated continuous culture of mammalian cells in suspension

A system has been developed for the continuous culture of mammalian cells in suspension. The system maintains constant cell concentrations (monitored as the degree of light scattering) over a wide range of previously selected values by automatic additions of known amounts of medium and simultaneous withdrawals of equal volumes of cell suspension.

Absence of translational control of histone synthesis during the HeLa cell life cycle

The cell-free synthesis of histone-like polypeptides has been achieved using a selected class of small polyribosomes as the only particulate fraction. This synthesis is prevented if the deoxyribonucleic acid (DNA) inhibitor, cytosine arabinoside, is added to the cells prior to disruption, and it is not detected when the cytoplasm used is derived from postmitotic (G(1)) cells. When the 100,000 g supernate from pure metaphase populations was compared with that from S phase cells, the cell-free synthesis of histone-like polypeptides in the presence of S phase polyribosomes remained unchanged. These data suggest that, except for the histone messenger RNA-ribosome complex, the cytoplasmic factors requisite for histone synthesis are present throughout the cycle, and that the shut-off of this synthesis is not under translational control.