Translation of Messenger RNA for Histones from HeLa Cells by a Cell-Free Extract from Mouse Ascites Tumor

7-9S RNA has been isolated from polyribosomes of HeLa S-3 cells in S phase. These RNA species direct the synthesis in vitro of all five classes of human histones when they are added to a protein-synthesizing system derived from mouse ascites tumor cells. The histones synthesized in vitro have been identified by two kinds of acrylamide gel electrophoresis, and by paper electrophoresis of tryptic digests. By use of the ratio of tyrosine to tryptophan incorporation as an index of contamination, it was determined that less than 10% of the 7-9S RNA is translated into proteins other than histones.