The nucleolus in various phases of growth of mouse lymphoma L5178Y cells in culture.

The number of nucleoli in cultures of murine lymphoblasts L5178Y was investigated. It was found that during the cell cycle the number of nucleoli changed significantly. Comparison of the course of the cell cycle phases measured by the rate of 3H-thymidine incorporation into DNA and the mitotic index suggests that lymphoblasts containing 2 nucleoli are characteristic of the peak of the S-phase, lymphoblasts with 1 nucleolus--for the G1 phase or the border G1/S, lymphoblasts with 3 or more nucleoli--for the phase preceding mitosis, presumably late S and G2.