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A cyclic-AMP-independent nuclear protein kinase has been purified from Dictyostelium discoideum amoebae. The purification procedure involves chromatography of DEAE-Sephadex, phosphocellulose and heparinSepharose. The purified enzyme phosphorylates threonine and serine of acidic proteins as casein and phosvitin. Phosphorylation of casein is stimulated by spermine. The kinase requires Mg2 + and can utilize both ATP and GTP as phosphoryl donors. Heparin is a potent inhibitor of the enzyme, being the protein kinase activity fully inhibited at concentrations of 0.5 pg/ml. One polypeptide of molecular mass 38 kDa was the major protein band present in the purified kinase preparation as estimated by NaDodSO, denaturing polyacrylamide gel electrophoresis. This band belongs to the protein kinase because it is the only one that is observed associated with the protein kinase activity when the enzyme preparation is centrifuged in glycerol gradients. The 38-kDa polypeptide is also the major product of autophosphorylation of the enzyme preparation. The enzymatic properties allow to classify the enzyme as a type-I1 casein kinase. However, its structural properties are different from the mammalian type-I1 casein kinases and make the D. discoideum enzyme more similar to the plants type-I1 casein kinases.Phosphorylation/dephosphorylation of proteins represents an important mechanism in the control of cellular processes, including the regulation of gene expression in eukaryotic cells I1,21.Among the enzymes that catalyze the postranslational phosphorylation of proteins are cyclic-nucleotide-dependent an independent protein kinases. Extensive investigations of CAMP-dependent protein kinases have shown that these enzymes mediate all of the biological effects of cyclic AMP. In contrast, little is known about the physiological role of the CAMP-independent protein kinases, although several types of these kind of enzyme have been characterized in different biological systems, mainly higher eukaryotes [3].The nuclear phosphorylation of chromatin-associated proteins, both histones and non histones, have been implicated in the regulation of gene transcription [4, 51. A cyclic-nucleotideindependent, polyamine-sensitive protein kinase has been involved in the control of transcription of ribosomal RNA genes by means of phosphorylation of RNA polymerase I [6] and some transcriptional factors [7].In the slime mold Dictyostelium discoideum a lot of effort has been dedicated to the study of the involvement of CAMPdependent protein kinases in the expression of its differentiation program. CAMP is the chemical agent that mediates aggregation of the amoebae [8] and it is also implicated in the regulation of latter stages of differentiation [9]. CAMPdependent protein kinases have been identified in D. discoideum both in vegetative cells [lo] and during differentiation [I 1, 121. Besides, the characterization of the regulatory subunit of a CAMP-dependent protein kinase has also been carried out using a photo-affinity probe [13]. However, the character...

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A purification procedure to obtain RNA polymerases I (or A) and II (or B) from Dictyostelium discoideum amoeba has been developed. The enzymes were solubilized from purified nuclei and separated by DEAE-Sephadex chromatography. RNA polymerases I and II were further purified by a second chromatography on DEAE-Sephadex followed by chromatographies on phosphocellulose and heparin-sepharose. The specific activities of purified RNA polymerases I and II are 92 units/mg protein and 70 units/mg protein, respectively. The subunit structure of both RNA polymerases were analyzed by polyacrylamide gel electrophoresis under denaturing conditions after glycerol gradient centrifugation of the enzymes. The putative subunits of RNA polymerase I have molecular weights of 180 000, 125 000, 43 000, 40,000, 34 000, 31 000, 25 000, 19 000, 17 000 and 14 000. The putative subunits of RNA polymerase II have molecular weights of 200 000 (170 000), 130 000, 33 000, 25 000, 19 000, 17 000, 15 000, 13 000. There are three polypeptides with common molecular weight in Dictyostelium RNA polymerases I and II. The subunit of 25 000 daltons of both enzymes has common immunological determinants with RNA polymerase II from crustacean Artemia.