title: G1 and S phase mammalian cells synthesize histones at equivalent rates.
abstract: To determine the effect of cell cycle position on protein synthesis, synchronized cell populations were metabolically labeled and the synthesis of the basic proteins, including histones, was examined by two-dimensional gel electrophoresis. Exponentially growing S49 mouse lymphoma or Chinese hamster ovary (CHO) cells were separated into G1 and S phase populations by centrifugal elutriation, selective mitotic detachment, fluorescence-activated cell sorting, or a combination of these, and pulse-labeled with radiolabeled amino acids. The histone proteins, both free and chromatin-bound, were completely resolved from some 300 other basic polypeptides in whole-cell lysates by a modification of the NEPHGE technique of O'Farrell, Goodman and O'Farrell (1977). Comparisons of matched autoradiograms from samples of G1 and S phase labeled cells revealed an equivalent rate of histone synthesis through the cell cycle of both S49 and CHO cells. Nuclei isolated from G1 phase S49 cells that were pulse-labeled containing between 13 and 15% of the newly synthesized nucleosomal histones present in S phase nuclei. Nuclei prepared from G1 phase cells that were pulse-labeled and then chased for 5 hr contained more than 90% of the labeled nucleosomal histones present in whole-cell lysates. It therefore seems likely tha differential alterations in the rate of histone synthesis do not occur to a significant degree as cells proceed through the cycle, but the association of newly synthesized histones with DNA takes place after the onset of DNA replication.
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000032:analysis; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis; D006657:Histones / Q000032:analysis / Q000096:biosynthesis*; D007399:Interphase; D007700:Kinetics; D051379:Mice; D014176:Protein Biosynthesis
chemical_list: D006657:Histones; D004247:DNA