Open AccessThe Effect of α‐Amanitin and (NH 4 ) 2 SO 4 on RNA Synthesis in Nuclei and Nucleoli Isolated from Physarum polycephalum at Different Times during the Cell Cycle
Author(s) -
Grant William D.
Publication year - 1972
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1972.tb01961.x
Subject(s) - nucleolus , physarum polycephalum , mitosis , rna , physarum , biology , microbiology and biotechnology , ribosomal rna , biochemistry , nucleus , gene
Nuclei isolated from various points in the mitotic cycle were examined for RNA synthesis in the presence of Mg 2+ or Mn 2+ + (NH 4 ) 2 SO 4 . A peak of activity 2.5—3 h after mitosis was only slightly increased by Mn 2+ + (NH 4 ) 2 SO 4 over that in the presence of Mg 2+ , and inhibited some 50% by low levels of α‐amanitin in the presence of either Mg 2+ or Mn 2+ + (NH 4 ) 2 SO 4 . A G2 peak of activity 2.5—3 h before mitosis was 100% increased by Mn 2+ + (NH 4 ) 2 SO 4 over that observed in the presence of Mg 2+ , the increase being completely sensitive to low levels of α‐amanitin, whereas the Mg 2+ activity remained insensitive. Nucleoli isolated some 2.5—3 h before mitosis exhibited RNA synthesis which was unstimulated by Mn 2+ + (NH 4 ) 2 SO 4 and insensitive to α‐amanitin. Similarities in RNA synthesis in isolated nucleoli and isolated G2 nuclei in the presence of Mg 2+ with respect to pH optima and actinomycin‐D sensitivity were observed. It is concluded that there is a high basal level of α‐amanitin‐insensitive RNA synthesis activity which is nucleolar and therefore probably ribosomal, rising to a peak some 2.5—3 h before mitosis, and a major peak of α‐amanitin‐sensitive nucleoplasmic RNA synthesis activity some 2.5—3 h after mitosis, thereafter dropping to a low level.