Biomedical subjects
Publications and source records attributed to G N Dessev.
The past 18 months have seen significant advances in our knowledge of the constituents of the nuclear envelope, their interactions during interphase and the mechanisms involved in their mitotic dynamics. Although most of the new data are in general agreement with, and contribute detail to, our traditional image of the nuclear envelope, a few observations appear to mark the beginning of new and important directions in research.
The nuclear lamina of surf clam oocytes contains dimers of 67-kDa lamin which are stabilized by both noncovalent interactions and disulfide bonds. The latter can be reduced but re-form when the reducing agent is removed. The cysteine residues involved in these disulfide bonds are inaccessible to alkylating agents unless the protein is unfolded in urea. During nuclear envelope breakdown the lamin is released as a mixture of oligomers in which disulfide-stabilized dimers are associated noncovalently with lamin monomers. Concurrent with solubilization, both dimers and monomers are phosphorylated to a similar extent, indicating that the interactions which maintain these complexes are not destabilized by lamin phosphorylation. Our results suggest the existence of two types of interactions between the lamin molecules in the polymer, which react differently to phosphorylation during nuclear envelope breakdown.
1. The effect of gamma-irradiation (4000rd) on the synthesis of ribosomal (pre-rRNA) and heterogeneous nuclear RNA (pre-mRNA) in normal and in regenerating rat liver was studied by using 40 min labelling with [6(-14)C]orotic acid. 2. Partial hepatectomy caused a sharp transient increase in the specific radioactivity of the endogenous low-molecular-weight RNA precursors in the livers of both normal and irradiated rats. Irradiation of intact animals did not affect the pool. 3. Irradiation enhanced the synthesis of pre-rRNA for at least 12h. The synthesis of pre-mRNA was also enhanced, but only in the first 3h after irradiation. 4. Partial hepatectomy strongly stimulated the synthesis of both pre-rRNA and pre-mRNA. 5. The synthesis of pre-rRNA was enhanced also in regenerating liver of animals irradiated before or after the operation. The conclusion can be drawn that the early increase in the synthesis of ribosomal RNA is a non-specific cellular response to different injuring factors. 6. The only case where irradiation caused an early inhibition of RNA synthesis was that of pre-mRNA in regenerating liver. This supports the hypothesis that ionizing radiation does not suppress the transcription per se but affects the mechanisms of activation of new genes (cellular programming).