"Active" two-dimensional electrophoresis of rat liver DNA-polymerase alpha

Protein profiles of the Chinese hamster ovary cells in the resting and proliferating stages

Identification and characterization of the proteins that regulate the transition from the resting stage (G0) through G1 to S phase of the cell cycle are of central importance to understand the control of cell proliferation and chromosome replication. Unlike in lower organisms, where relatively small numbers of key factors are involved in this process, the factors involved in the same control mechanisms in mammalian systems are much more complex. Furthermore, accumulating lines of evidence now suggest that the nuclear matrix and chromatin organization also play an essential role for the cell cycle control in mammalian cells. To gain a better understanding of the overall dynamics and changes of the protein factors in the context of matrix/chromatin organization, we examined the protein profiles of the Chinese hamster ovary (CHO) cells in different cell cycle compartments. The methods used in this study included subcellular fractionations (cytosol, nuclear extraction, chromatin, and nuclear matrix), two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), silver staining, and immunoblotting. As expected, significant changes of protein profiles were observed when cells entered into proliferating stages from G0. Among approximately 1200 protein spots analyzed by 2-D PAGE, at least 12 showed marked increase or decrease at this transitional period. Further cell-cycle progression from G1 to S phase showed less dramatic changes of overall protein protile. However, the profile of certain proteins showed rather dramatic changes of their subcellular localization during this transitional period. In particular, the levels of proliferating cell nuclear antigen (PCNA) in the nuclear matrix and chromatin dramatically increased in mid-G1 and in the beginning of S phase, respectively, while the overall PCNA level was relatively constant throughout the cell cycle.

Active dissociation of the fluorescent dye Hoechst 33342 from DNA in a living cell: who could do it?

It is assumed that DNA in mammalian cells is a dynamic conformationally unstable system. This instability provides the cell with a mechanism for dissociating a large number of substances that bind tightly but not covalently to DNA. Among these is the fluorescent dye Hoechst 33342, which binds to DNA in the minor groove. We have selected cell lines with a high capability for active dissociation of Hoechst 33342. Comparative protein analysis of these lines by means of two-dimensional (2-D) electrophoresis was performed. Cell and nuclear proteins were analyzed from these and normal strains. A few proteins with significantly changed quantities have been found. The preliminary search of the 2-D database allowed us to identity some known and unknown cellular proteins that could participate in active dissociation of the dye from DNA.