Multiple Forms of DNA‐Dependent RNA Polymerase I from Immature Chick Liver

Abstract

1. We found that a single injection of 17P-estradiol into immature chicks resulted within 24 h in a 2-fold increase of the transcriptional capacity of liver nuclei which involved both endogenous RNA polymerase I and I1 activities. Similarly, RNA polymerase activity I of purified nucleoli was also doubled.2. During purification of RNA polymerase I from controls and treated chicks the difference in activity was almost completely lost.3. RNA polymerase I could be resolved into two forms, IA and IB, on CM-Sephadex. Form IA increased and form IB decreased after estrogen treatment while the sum of the two remained constant. Form IA sedimented more slowly than form IB in glycerol gradients and was predominant in purified nucleoli.4. These observations suggest that there may be an equilibrium between the two forms of RNA polymerase I which may change in order to produce the translational shift-up which occurs after estrogen treatment.Multiplicity of DNA-dependent RNA polymerase has been shown to exist in many eukaryotic systems [l -41. The three major classes can be distinguished on the basis of differences in chromatographic properties, structure, a-amanitin sensitivity, salt and cation requirements and intracellular localization, as recently reviewed by Chambon [5]. This multiplicity suggests that specific genes or groups of genes might be transcribed by different RNA polymerases. Sufficient data have now accumulated to show that the nucleolar RNA polymerase I (or A) insensitive to a-amanitin synthesizes ribosomal RNA [6,7]. RNA polymerase I1 (or B) synthesizes heterogenous DNA-like RNA [8] and more recently the role of enzyme I11 (or C) in the synthesis of 5-S ribosomal RNA and tRNA has become known [9]. The relative proportion of class I, I1 and 111 varies among different cell types and under different physiological or metabolic conditions [ 10,113. In addition, each of these classes of DNA-dependent RNA polymerases does not always consist of one particular enzyme : there exists multiple forms of enzymes having the same requirements and identical functions but different subunits [9, this may relate to the very complex and by no means resolved mechanism of regulation of transcription.Modification of transcription by hormonal action is by now an established means to study its possible regulating factors. 17P-Estradiol injected into immature chicks induces in the liver within hours the synthesis of vitellogenin, the precursor of egg yolk protein [15-371. In correlation with the production of vitellogenin, one could observe an increased synthesis of polysomal RNA [15,18], a large amount of vitellogenin messenger RNA [19] and a net synthesis of ribosomal RNA concomitant with an increase in the elongation factors of translation EF-1 and EF-2 [20]. Our main interest focuses on the observed shift-up of the translational machinery and the work presented here concerns the changes of RNA polymerase I after estrogen treatment of immature chicks in relation to the transcription of the ribosomal genes. We wish to report here th...

Characterization of chick liver chromatin and analysis of its in vitro transcription products

“…26 Ci/mmol) were from The Radiochemical Centre (Amersham, U.K.) and [y32Plguanosine 5'-triphosphate (spec.act. [15][16][17][18][19][20][21][22][23][24][25] Ci/mmol) was from the New England Nuclear Corporation (Boston, Mass.). All other chemicals not mentioned were of analytical grade.…”