Effect of thyroid hormone on the phosphorylation of 110k proteins and the activity of protein kinase NII of rat liver nucleoli.

When rat liver nucleoli were incubated with [gamma-32P] ATP, it was found that 110k proteins were predominantly phosphorylated. The phosphorylation of 110k proteins was decreased by thyroidectomy to about 80% of the normal level and restored 12 h after the injection of triiodothyronine. The activity of nucleolar protein kinase NII which is responsible for phosphorylation of 110k proteins was also increased by about 20-50% after injecting triiodothyronine into thyroidectomized rats. The hormone-stimulated enhancement in the phosphorylation of 110k proteins and protein kinase NII in nucleoli were abolished within 1 h after an injection of cycloheximide, without any change in the amount of the proteins.