Nuclear-cytoplasmic relationships in human cells in tissue culture: IV. A study of some aspects of nucleic acid and protein metabolism in enucleate cells

Abstract

Enucleate pieces of cytoplasm were prepared from human amnion cells in tissue culture by a method of microsurgery. Vital activities of the fragments were retained for 10–30 h. One of several amino acids or RNA precursors labeled with 14C was added to the culture medium just before or just after preparation of a group of enucleate cytoplasmic fragments. When about half the fragments had “died”, the surviving enucleates were fixed and examined by autoradiography for evidence of incorporation of the labeled compound. Amino acids were incorporated as actively by enucleate cytoplasm as by cytoplasm of complete cells. This incorporation could be blocked by excess label-free L-isomers of the corresponding labeled amino acid but not by the label-free D-isomer. RNA precursors were not incorporated by enucleate cytoplasmic fragments in detectable amount, although neighboring intact cells incorporated the precursors actively into cytoplasm. The conclusions reached are (a) that protein synthesis continues in enucleate cytoplasm of mammalian cells, but (b) that RNA synthesis stops or is so slight as to escape detection by these methods. These data add to the evidence that cytoplasmic RNA is derived chiefly from the nucleus. The labeled precursors used were: [ 14C]adenine, [ 14C]uridine, L-[ 14C]glutamic acid, L-[ 14C]leucine, L-[ 14C]phenylalenine and DL-[ 14C]tryptophan; [8- 14C] adenylic acid was also used.