Cyclin (PCNA, auxiliary protein of DNA polymerase delta) is a central component of the pathway(s) leading to DNA replication and cell division

Cell cycle-associated change in the expression of the proliferation-sensitive and heat-shock protein hs x 70 (IEF14): increased synthesis during mitosis

The major heat-inducible protein of transformed human amnion cells (AMA) has been identified as the proliferation-sensitive polypeptide IEF14 (Mr 66 kDa; HeLa protein catalogue). From its mobility in two-dimensional gels (Mr and pI) as well as from the fact that this protein is immunoprecipitated by mAb C92 F3-5 (W. J. Welch, and J. P. Suhan, (1986) J. Cell Biol. 103, 2035-2052), we concluded that this polypeptide is either closely related or identical to the 72 kDa inducible stress human protein hs X 70 (H. R. B. Pelham (1986) Cell 46, 959-961). It is further shown that in AMA cells the rate of synthesis of this protein increases preferentially during mitosis. These results provide further evidence suggesting that the levels of hs X 70 can be modulated by mechanisms independent of heat shock.

Do DNA polymerases delta and alpha act coordinately as leading and lagging strand replicases?

The activity ratio of DNA polymerases delta and alpha in calf thymus was found to be invariably 1:1, irrespective of extraction procedure (8 types) and subcellular localization (cytoplasm, nucleus and microsomes). This was established by separation of the two forms by hydroxyapatite chromatography and by their response to specific inhibitors and monoclonal antibodies. This finding supports the dimeric DNA polymerase model [(1980) J. Biol. Chem. 255, 4290-4303], which proposes that DNA polymerases delta and alpha act coordinately as leading and lagging strand enzymes, respectively, at the replication fork.

Progressin: a novel proliferation-sensitive and cell cycle-regulated human protein whose rate of synthesis increases at or near the G1/S transition border of the cell cycle

A novel proliferation-sensitive and cell cycle-specific basic protein, termed progressin (Mr = 33,000), has been identified in proliferating human cells of epithelial, fibroblast and lymphoid origin. Progressin is synthesized almost exclusively during the S-phase of transformed human amnion cells (AMA). Increased synthesis of this protein is first detected late in G1, at or near the G1/S transition border, reaches a maximum in mid to late S-phase, and declines thereafter. Contrary to histones, progressin synthesis is not coupled to DNA replication. As expected for an S-phase-specific protein, no detectable synthesis of progressin was observed in non-proliferating human MRC-5 fibroblasts and epidermal basal keratinocytes. Elevated, but variable levels of this protein were observed in proliferating normal fibroblasts and transformed cells of fibroblast, epithelial and lymphoid origin. Taken together the above observations suggest that progressin may be a component of the common pathway leading to DNA replication and cell division.