Histone composition and core histone acetylation of transcriptionally active ribosomal chromatin of Physarum polycephalum

In situ EcoRI digestion of ribosomal gene chromatin in nucleoli of Physarum polycephalum releases a fragment of the transcribed part of the rRNA gene as shown by hybridization and psoralen crosslinking. In contrast to whole nucleoli, the active ribosomal chromatin fragment does not contain H1, H2A and H2B, but only H3 and H4. Comparison of the acetylation of histones in nuclei, nucleoli and active ribosomal chromatin does not reveal significant differences. These results suggest that the lack of H1, H2A and H2B is a prerequisite for in vivo transcription of the ribosomal gene chromatin of Physarum.