A protein that accumulates during starvation in Tetrahymena nuclei

Tetrahymena pyriformis was starved in 50 mM Tris-HCl, pH 7.5, at 28 degrees C. The number of cells did not change appreciably under the starvation conditions. Nuclear proteins of unstarved cells and cells starved for 1, 2, 4, and 7 d were analyzed by SDS-polyacrylamide gel electrophoresis. Most of the large amount of nonhistone proteins present in the unstarved cell nucleus disappeared with the starvation time. However, the relative amounts of the high mobility group protein and histones did not change appreciably. On the other hand, a protein with a molecular weight of ca. 16,000 gradually accumulated in the nucleus on starvation. This protein was extracted with 0.25 M HCl, but was not soluble in 0.5 M perchloric acid. The amino acid composition and molecular weight of this protein were similar to those of HMG protein LG-2 of T. thermophila. Some lysyl endopeptidase peptides of this protein were found to have amino acid sequences present in LG-2, thus we tentatively named it an LG-2-like protein.