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Multiple phosphorylation sites at the C-terminus regulate nuclear import of HCMV DNA polymerase processivity factor

Gualtiero Alvisi1, Oriano Marin, Gregory Pari

  • 1Department of Hematology and Oncology Lorenzo e Ariosto Seràgnoli, University of Bologna, Medical School, Bologna, Italy. gualtiero.alvisi@unipd.it

Virology
|July 12, 2011
PubMed

Insights

Human cytomegalovirus (CMV) DNA polymerase processivity factor, phosphoprotein ppUL44, undergoes complex phosphorylation. This regulates its nuclear transport, crucial for viral replication.

Area of Science:

  • Virology
  • Molecular Biology
  • Cellular Biology

Background:

  • Phosphoprotein ppUL44 is essential for human cytomegalovirus (CMV) DNA polymerase processivity and viral replication.
  • The role of ppUL44 phosphorylation by viral kinase pUL97 and its impact on ppUL44 activity remain largely unknown.

Purpose of the Study:

  • To identify ppUL44 phosphorylation sites and elucidate the effects of phosphorylation on its nuclear transport during CMV infection.

Main Methods:

  • Transient expression of ppUL44 in mammalian cells.
  • Coimmunoprecipitation assays to identify interacting cellular kinases.
  • Site-directed mutagenesis to investigate phosphorylation site function.

Main Results:

  • Protein kinase CK2 (CK2) specifically phosphorylates S413 on ppUL44, initiating a phosphorylation cascade at S418 (by CK1) and S415 (by CK2).
  • Phosphorylation of S413, S415, and S418 by CK2/CK1 enhances ppUL44 nuclear accumulation.
  • Phosphorylation at T427 within the nuclear localization signal (NLS) significantly reduces nuclear import.

Conclusions:

  • Nuclear transport of ppUL44 is tightly regulated by complex phosphorylation events mediated by cellular kinases CK2 and CK1.
  • Differential phosphorylation of specific sites on ppUL44 fine-tunes its nuclear localization, impacting viral replication dynamics.

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