Phosphorylation of NF-I in vitro by cdc2 kinase

Nuclear factor I (NF-I) was purified to near homogeneity from Ehrlich ascites tumor cells. Mouse NF-I consisted of two peptides with relative molecular masses of 53 and 55 kDa and bound to the authentic NF-I site of the adenovirus DNA with no significant affinity with the CCAAT box. The purified protein was efficiently phosphorylated in a reaction containing immunoprecipitates with an anti-cdc2 kinase antibody. This phosphorylation was abolished when a synthetic peptide containing the consensus phosphorylation site by cdc2 kinase was added in excess to the reaction. These findings indicate that mouse NF-I is phosphorylated in vitro by the cdc2 protein kinase.