HYDROXYUREA: INHIBITORY EFFECT ON DNA METABOLISM

Hydroxyurea, hydroxyurethane, and dihydroxyurea inhibit incorporation of thymidine into the DNA of monolayers of HeLa cells. They do not affect incorporation of uridine into RNA or of leucine into protein. In contrast, hydroxylamine inhibits cellular incorporation of all three precursors: thymidine, uridine, and leucine. Hydroxyurea does not affect thymidine kinase, thymidylate kinase, or DNA polymerase reactions, but it does inhibit incorporation of cytidylic and guanylic acids into DNA in cell-free supernatants.

BETA-GALACTOSIDASE: INACTIVATION OF ITS MESSENGER RNA BY ULTRAVIOLET IRRADIATION

A brief exposure of Escherichia coli cells to an indutcer for beta- galactosidase results in the production of a messenger RNA which subsequently expresses itself as beta-galactosidase. Ultraviolet irradiation of cells after exposure to the inducer results in a decrease in the amount of beta-galactosidase formed. The messenger RNA formed during the brief exposure to inducer is evidently inactivated by the ultraviolet radiation. The decay of messenger RNA activity in irradiated cells has the same kinetics as that observed in unirradiated cells.

AMINO ACIDS AS PROTECTIVE COMPOUNDS IN ULTRAVIOLET-IRRADIATED HANSENULA WINGEI

Hunt, D. E. (Charles V. Chapin Hospital, Providence, R.I.). Amino acids as protective compounds in ultraviolet-irradiated Hansenula wingei. J. Bacteriol. 88:893-895. 1964.-"Prefeeding" Hansenula wingei with small concentrations of either tryptophan, cystine, tyrosine, phenylalanine, leucine, cysteine, threonine, isoleucine, ethionine, norvaline, or histidine protected this yeast against inactivating ultraviolet treatment. "Prefeeding" with methionine, proline, or alanine conferred little if any protection, and valine or serine caused this organism to be more sensitive to ultraviolet inactivation. A direct relation exists between the concentration of the protective amino acids and the number of surviving cells. The heterocyclic and aromatic amino acids are generally more protective than the corresponding aliphatic compounds. The diversity of the compounds as well as quantitative differences in the protection afforded by them suggest that they have different modes of action.

INTRANUCLEAR SITE OF HISTONE SYNTHESIS

The nucleolus is implicated as a site of synthesis of nuclear basic proteins. Some of these newly synthesized sized proteins derived from the nucleolus have been characterized chemically as histones.