Human papillomavirus type 6 E7 protein is a substrate in vitro of protein kinase C

The E7 proteins of 'low-risk' and 'high-risk' human papillomaviruses (HPV) are phosphorylated by casein kinase II. In this study, we report that the 'low-risk' HPV 6 E7 protein, but not the 'high-risk' HPV 16 E7 protein, can be phosphorylated in vitro on threonine at amino acid position 7 by protein kinase C. This is the first example of a qualitative biochemical difference between the HPV 6 E7 and HPV 16 E7 proteins.