HPV16 E7 phosphorylation in fission yeast: characterization and biological effects

Abstract Human papillomavirus type 16 E7 protein (HPV-16 E7), synthesised in Schizosaccharomyces pombe , is both phosphorylated and targeted to the nucleus [Tommasino et al., Gene 93 (1990) 265–270] as is E7 protein synthesized in primate cells. Further analysis of E7 expression in fission yeast indicates that: ( i ) E7 protein synthesised in S. pombe is phosphorylated only on the Ser residues which are part of a casein kinase II consensus site, as it has been shown to be the case in human cells, and is tightly associated with the nuclear matrix; ( ii ) synthesis of wild type, phosphorylated E7 is responsible for a significant increase in S. pombe doubling time; and ( iii ) E7 phosphorylation is not required for the tight association of the protein with the nuclear matrix, but E7 mutants, in which one (Ser 31 ) or both phosphorylated serines (Ser 31 and Ser 32 ) have been substituted, lack any effect on cell-cycle duration.