Histone phosphorylation during repression of proliferation in a lower eucaryote Physarum polycephalum.

Nutrient depletion causes a rapid drop in transcription and completely inhibits DNA replication in plasmodia of a slime mold Physarum polycephalum. These events are accompanied by progressive dephosphorylation of histone H3 and no change in the state of phosphorylation of the bulk of histone H1. This shows that the compaction of chromatin associated with transcriptional inactivation does not require phosphorylation of H3 and suggests that the level of basal phosphorylation of H1 is not correlated with the intensity of transcription or DNA replication. An increase in the proportion of unmethylated versus methylated H1 is visible, suggesting a role for this H1 modification in the regulation of chromatin functioning.