The DNA replication schedule is not affected in a division blocked mutant of Tetrahymena thermophila.

Abstract

Cell cycle parameters (generation time, G1, S, G2 period) have been determined for the temperature sensitive mutant mol a of Tetrahymena thermophila in which the cell division and macronuclear division are blocked at a restrictive temperature, whereas the first stages of cell division occur. It was found that in cells blocked in this way DNA replication continues in a rhythmical pattern. Replication during the S period leads to a doubling of the macronuclear DNA content. The generation time is shorter at a restrictive temperature but there is no difference between mutant and wild-type cells. The duration of the cell cycle phases changes proportionally to the generation time. Again, in this respect there is no significant difference between mol a and wild type cells at a restrictive and permissive temperature. These findings indicate that the timing and completion of macronuclear DNA replication is not affected by the mutation at the mol locus and is not directly dependent on a preceding cell and macronuclear division.