Block of histone synthesis in isolated sea urchin cells actively synthesizing DNA

The synthesis of DNA and histones are normally coupled. Only a few exceptions have been found. Dissociated cells from sea urchin embryos stop DNA synthesis, but resume it after trypsin treatment. It was of interest, therefore, to examine whether the synthesis of histones is similarly affected. Sea urchin embryos were dissociated from swimming blastulae and the cells so obtained were divided into two batches, one of which was treated with trypsin. Normal embryos from the same culture were used as controls. It was found that, in the dissociated cells, histone synthesis ceases, but unlike DNA, its synthesis is not resumed after treatment with trypsin.