Abstract
Abstract The phosphorylation of non-histone nuclear proteins has been studied in HeLa S-3 cells during synchronous growth. The uptake of [32P]orthophosphate into individual protein bands separated on sodium dodecyl sulfate polyacrylamide gels varies at different stages in the cell cycle while the banding patterns themselves are remarkably constant. Rates of phosphate uptake into most major phosphoprotein species are increased during the early G1 and early S phases and are minimal during the late G2 to M period. The turnover of previously incorporated phosphoryl groups during a cold chase following a 23-hour exposure to [32P]orthophosphate shows that some proteins lose their phosphoryl residues much more rapidly than do others. The halflives vary from 5 to 12 hours, with an over-all half-life of 6.7 hours. In contrast, the 14C specific activity of the proteins falls to 50% of the original activity in about 25 hours. The retention of [32P]phosphate is a more sensitive index of differential phosphoryl group turnover in different nuclear acidic proteins than is the uptake of [32P]phosphate in short term labeling experiments. If the nuclear phosphoproteins play a role in differential transcription during the cell cycle, changes in phosphorylation would appear to be more significant than changes in relative concentrations of individual protein species.
Highlights
The phosphorylation of non-histone nuclear proteins has been studied in HeLa S-3 cells during synchronous growth
The turnover of previously incorporated phosphoryl groups during a cold chase following a 23-hour exposure to [“‘PIorthophosphate shows that some proteins lose their phosphoryl residuesmuch morerapidly than do others
Composition of HeLa Nuclei at Di$erent Stages in Cell Cycle-Nuclear protein and DNA contents have been examined in synchronously growing HeLa S-3 cells at different times after release from a double thymidine block [25, 26]
Summary
The phosphorylation of non-histone nuclear proteins has been studied in HeLa S-3 cells during synchronous growth. The experiments to be described deal with changes in the metabolic activities of nuclear phosphoproteins during the replication cycle of synchronously growing mammalian cells Interest in this classof proteins stemsfrom observationsthat they show strong indications of involvement in the positive control of geneactivity (e.g.1-13). The question arises as to whether the nuclear phosphoproteins are altered at times of gene activation and repression during the cell cycle It is known, for example, that the synthesis of RNA in synchronously dividing cells is suppressed during mitosis. Preliminary studies of phosphorylation of HeLa nuclear proteins during the cell cycle indicate that the rate of phosphorylation is maximal in the early S phase and decreases in the late S and G2 phases when RNA synthesis is reduced [23]. The present study is a detailed analysis of the uptake and turnover of phosphate in the phenol-soluble nuclear acidic proteins of synchronously and nonsynchronously growing HeLa S-3 cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
