Utilization of pre-existing messenger RNAs for nonhistone chromosomal protein synthesis in WI-38 human diploid fibroblasts

Abstract

Contact-inhibited monolayers of WI-38 human diploid fibroblasts show an increase in chromatin template activity within 1 h following stimulation to proliferate. Direct evidence that nonhistone chromosomal proteins are responsible for this increased transcriptional activity of the genome comes from previous studies which demonstrate that the template activity of chromatin reconstituted with nonhistone chromosomal proteins from WI-38 cells 1 h following stimulation is higher than the template activity of chromatin reconstituted with nonhistone chromosomal proteins from contact-inhibited cells. The present studies indicate that there is an increase in the amount of two specific newly synthesized molecular weight classes of nonhistone chromosomal proteins in chromatin 1 h following the stimulation of contact-inhibited WI-38 cells to proliferate and that the synthesis of these nonhistone chromosomal proteins occurs in the absence of new RNA synthesis. The possibility that such nonhistone chromosomal protein synthesis early during the prereplicative phase of the cell cycle may be regulated at the translational level is discussed.