TY - JOUR
T1 - Reverse transcription-associated dephosphorylation of hepadnavirus nucleocapsids
AU - Perlman, David H.
AU - Berg, Eric A.
AU - O'Connor, Peter B.
AU - Costello, Catherine E.
AU - Hu, Jianming
PY - 2005/6/21
Y1 - 2005/6/21
N2 - Hepatitis B viruses are pararetroviruses that contain a partially dsDNA genome and replicate this DNA through an RNA intermediate (the pregenomic RNA, pgRNA) by reverse transcription. Viral assembly begins with the packaging of the pgRNA into nucleocapsids (NCs), with subsequent reverse transcription within NCs converting the pgRNA into the characteristic dsDNA genome. Only NCs containing this dsDNA (the so-called "mature" NCs) are enveloped by the viral envelope proteins and secreted as virions; "immature" NCs, i.e., those containing pgRNA or immature reverse transcription intermediates, are excluded from virion formation. This phenomenon is thought to be caused by the emergence of an intrinsic maturation signal only on the mature NCs. To define the maturation signal, we have devised a method to separate mature from immature duck hepatitis B virus NCs and have compared them to NCs derived from secreted virions. Detailed mass spectrometric analyses revealed that the core protein from immature NCs was phosphorylated on at least six sites, whereas the core protein from mature NCs and that from secreted virions was entirely dephosphorylated. These results, together with the known requirement of core phosphorylation for pgRNA packaging and DNA synthesis, suggest that the NC undergoes a dynamic change in phosphorylation state to fulfill its multiple roles at different stages of viral replication. Although phosphorylation of the NCs is required for efficient RNA packaging and DNA synthesis by the immature NCs, dephosphorylation of the mature NCs may trigger envelopment and secretion.
AB - Hepatitis B viruses are pararetroviruses that contain a partially dsDNA genome and replicate this DNA through an RNA intermediate (the pregenomic RNA, pgRNA) by reverse transcription. Viral assembly begins with the packaging of the pgRNA into nucleocapsids (NCs), with subsequent reverse transcription within NCs converting the pgRNA into the characteristic dsDNA genome. Only NCs containing this dsDNA (the so-called "mature" NCs) are enveloped by the viral envelope proteins and secreted as virions; "immature" NCs, i.e., those containing pgRNA or immature reverse transcription intermediates, are excluded from virion formation. This phenomenon is thought to be caused by the emergence of an intrinsic maturation signal only on the mature NCs. To define the maturation signal, we have devised a method to separate mature from immature duck hepatitis B virus NCs and have compared them to NCs derived from secreted virions. Detailed mass spectrometric analyses revealed that the core protein from immature NCs was phosphorylated on at least six sites, whereas the core protein from mature NCs and that from secreted virions was entirely dephosphorylated. These results, together with the known requirement of core phosphorylation for pgRNA packaging and DNA synthesis, suggest that the NC undergoes a dynamic change in phosphorylation state to fulfill its multiple roles at different stages of viral replication. Although phosphorylation of the NCs is required for efficient RNA packaging and DNA synthesis by the immature NCs, dephosphorylation of the mature NCs may trigger envelopment and secretion.
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U2 - 10.1073/pnas.0502138102
DO - 10.1073/pnas.0502138102
M3 - Article
C2 - 15951426
AN - SCOPUS:21144448515
SN - 0027-8424
VL - 102
SP - 9020
EP - 9025
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 25
ER -