Histone synthesis in vitro on HeLa cell microsomes. The nature of the coupling to deoxyribonucleic acid synthesis.

Microsomes isolated from HeLa cells during DNA replication synthesize electrophoretically identifiable histones in vitro. Inhibition of DNA synthesis with hydroxyurea or high concentrations of thymidine results, within 30 min, in a termination of histone synthesis in vitro. Under these conditions, the labeling of other acid-soluble, nonhistone proteins is not affected. Inhibition of RNA synthesis with actinomycin D or Z-mercapto-I-(@-4-pyridethyl)benzimidazole in whole cells up to 90 min does not interfere with the histone synthesis in vitro. A rapidly labeled RNA with an approximate sedimentation constant of 8 to 9 S is connected with the microsomal fraction only when histones are being synthesized. The existence is inferred of a short-lived factor which facilitates the translation of histone messenger RNA in the cytoplasm.