Effects of hydroxyurea on Crithidia fasciculata.

Hydroxyurea (HU) inhibits increase in cell number in cultures of Crithidia fasciculata. Complete inhibition is produced by 8 mM and higher concentrations. If HU is not removed, population growth resumes in 45-50 h; if HU is removed, partially synchronous growth occurs through 2 cycles. During HU inhibition, the rate of DNA synthesis is reduced to 1% of that in exponentially growing cultures; protein and RNA syntheses continue at slightly reduced rates. Mean cell size and protein and RNA contents per cell increase; rate of oxygen consumption per mg cell protein remains constant. The behavior of a culture upon addition of HU and upon its removal agrees with predictions based on the hypothesis that the only direct effect of HU is to block DNA synthesis. The synchrony produced by HU is judged satisfactory for investigations of kinetoplast and nuclear replication but not for biochemical characterization of other aspects of the cell cycle.