Rat liver nuclear protein kinases NI and NII. Purification, subunit composition, substrate specificity, possible levels of regulation.

Rat liver nuclear protein kinases NI and NII have been purified to homogeneity by an improved method. This method includes a casein-phosvitin-Sepharose column step, which separates the enzymes from the other chromosomal non-histone proteins, and a gel filtration at high ionic strength in the presence of a high concentration of protease inhibitors to separate the two enzymes from each other. NI has an apparent molecular mass of approximately 50 kDa and is composed of a single subunit.

Iron stimulation of ferritin synthesis. II.-Involvement of polysomal kc1 extracts in the mechanism of stimulation.

The iron stimulation of ferritin synthesis is a translational phenomenon. Iron acts through a modification of the microsomal apparatus as shown previously. In the present study we have shown that the factor(s) involved in this stimulation are present in the KC1 extracts from polysomes of iron-treated rats.