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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 2-mercapto-1-(β-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.
Gallwitz et al. (Sat,) studied this question.