Nuclear proteins involved in cell division in the ciliate, Tetrahymena

For the purpose of clarifying the presence of nuclear proteins which may induce cell division, we conducted experiments using ciliate Tetrahymena which can be synchronized at the G2 phase in the cell cycle easily by periodic heat shock treatment (HST): We obtained proteins from the nuclei isolated from the cells grown at the early mid log-phase, at the G2 phase (60 min) and at the G1 phase (150 min), after HST. The proteins were studied by comparing the spots separated by isoelectric point, 10-20% gradient SDS two-dimensional electrophoresis. As a result, in comparison with the intranuclear protein at the log-phase, the proteins at the G2 phase showed a marked increase, but with no great change in the electrophoretic pattern. Meanwhile, the proteins at the G1 phase differed greatly from those at the G2 phase not only in the quantitative changes, but in the electrophoretic patterns. It is considered that the level of the accumulation of the nuclear proteins which should be closely involved in cell division must increase markedly at the G2 phase and decrease at the G1 phase. We confirmed the presence of four proteins: pI 5.8 MW 68 kDa, pI 6.1 MW 75 kDa, pI 8.6 MW 48 kDa and pI 6.6 MW 57 kDa, and then prepared monoclonal antibodies using these nuclear proteins as antigens. Among them, the antibody (IgM) against the pI 8.6 MW 48 kDa polypeptide (p48) was recognized the nuclei by indirect immunofluorescence in ancellular system at the S, G2 and the mid-M phases. However, nuclei at the late M and G1 phases were not stained.(ABSTRACT TRUNCATED AT 250 WORDS)