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  • Title: [Sequential activation of various types of nuclear RNA polymerases of rat liver cells during the process of DNA synthesis induction by cycloheximide].
    Author: Alesenko AV, Krasil'nikov VA, Boĭkov PIa, Todorov IN.
    Journal: Biokhimiia; 1984 Mar; 49(3):455-9. PubMed ID: 6722215.
    Abstract:
    The dynamics of changes in the activity of RNA polymerases I and II (EC 2.7.7.6) and the activities of free and bound forms of RNA polymerase II in isolated rat liver nuclei after a singular injection of sublethal dose of cycloheximide (CHI) was studied. Activation of RNA polymerases occurs in three steps. The first step (1--2 hours after CHI injection) coincides with inhibition of protein synthesis and predominant activation of both forms of RNA polymerase II. The second step (6--24 hours after CHI injection) is characterized by de novo protein synthesis and activation of RNA polymerase I and RNA polymerase II. The third step (36--48 hours after CHI injection) witnesses activation of both RNA polymerases which coincides with the beginning of stimulation of DNA replication. It is assumed that this step is coupled with the synthesis of a special form of RNA polymerase, RNA polymerase IV, which is responsible for transcription of genes synthesizing various chromatin components (histones, NHB, RNA prime). At all steps the activity of free RNA polymerase II remains at a sufficiently high level. Consequently, the activity of chromatin is limited by chromatin structure rather than by RNA polymerase II content in it. Presumably, such activation of various forms of RNA polymerase is essential for cell preparation for DNA replication.
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