Casein kinase II from rabbit reticulocytes is a tetramer with an alpha,alpha' beta 2 or alpha 2 beta 2 structure; the alpha subunits contain the catalytic activity, and the beta subunits are regulatory in nature [Traugh, J.A., Lin, W. J., Takada-Axelrod, F., & Tuazon, P. T. (1990) Adv. Second Messenger Phosphoprotein Res. 24, 224-229]. When casein kinase II is isolated from rabbit reticulocytes by a rapid two-step purification of the enzyme, both the alpha and beta subunits are phosphorylated to a significant extent. In vitro, purified casein kinase II undergoes autophosphorylation on the beta subunit. In the presence of polylysine and polyarginine, phosphorylation of the beta subunits is inhibited, and the alpha subunits (alpha and alpha') become autophosphorylated. The effectiveness of polylysine coincides with the molecular weight. With basic proteins, including a number of histones and protamine, autophosphorylation of both subunits is observed. With histones, autophosphorylation of each subunit can be greater than that observed with the autophosphorylated enzyme alone or with a basic polypeptide. Thus, the potential exists for modulatory proteins to alter the autophosphorylation state of casein kinase II. Taken together, the data suggest that phosphorylation of the alpha subunit of casein kinase II in vivo may be due to an unidentified protein kinase or due to autophosphorylation. In the latter instance, casein kinase II could be transiently associated with specific intracellular compounds, such as basic proteins, with a resultant stimulation of autophosphorylation.

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Elongation factor 1 (EF-1) consists of four subunits: the alpha subunit catalyzes the GTP-dependent binding of aminoacyl-tRNA to ribosomes while the beta, gamma, and delta subunits catalyze GDP/GTP exchange on EF-1 alpha. Phosphorylation of the beta subunit of EF-1 from rabbit reticulocytes by casein kinase II was stimulated up to 22-fold by polylysine, while basic proteins or polyarginine enhanced phosphorylation to a lesser extent. When physiological components of protein synthesis were examined as potential modulators of phosphorylation, ribosomal subunits had no effect, tRNA and poly(U) inhibited the phosphotransferase reaction, and GDP stimulated the initial rate of phosphorylation of EF-1 beta up to 3.8-fold; the degree of stimulation could be correlated with the amount of alpha subunit present in EF-1. No stimulation was observed with other nucleotides. Phosphorylation of EF-1 beta was on serine, and two-dimensional phosphopeptide mapping showed a single tryptic phosphopeptide in the presence of GDP or polylysine; the peptide was identical to that obtained with EF-1 phosphorylated in reticulocytes incubated with [32P]orthophosphate. EF-1 delta was also phosphorylated by casein kinase II, but only in the presence of GDP. Kinetic data showed GDP stimulated phosphorylation by increasing the Vmax with both the beta and delta subunits. The GDP-dependent stimulation of phosphorylation was specific for EF-1 and was not observed with calmodulin, beta-casein B, or c-Myc.(ABSTRACT TRUNCATED AT 250 WORDS)

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One subunit of EF-I or EF-Ifl7 from Artemia salina, wheat germ and rabbit reticulocytes is modified by casein kinase II. The subunit corresponds to the low Mr subunit of EF-1 (26000-36000) which functions along with a higher Mr subunit (46000~8000), to catalyze the exchange of GDP for GTP on EF-lct. The factor from Artemia and wheat germ is phosphorylated directly on serine by casein kinase II whereas a modulatory compound is required for phosphorylation of EF-1 from reticulocytes. Polylysine increases the rate of phosphorylation of EF-1 from reticulocytes by 24-fold; both serine and threonine are modified. This suggests that polylysine may be substituting for a physiological regulatory compound which modulates phosphoryation in vivo.