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Gene Review

HC-Pro  - 

Sweet potato feathery mottle virus

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Disease relevance of HC-Pro


High impact information on HC-Pro

  • Genetic crosses and segregation analyses revealed that a P1/ HC-Pro transgene suppressed PTGS of the GUS sequence [4].
  • By expressing PVY and CMV-encoded proteins in a PVX vector we have shown that the viral suppressors of gene silencing are the HCPro of PVY and the 2b protein of CMV [5].
  • Expression in transgenic plants of a construct with a large deletion in the 35 kd protein coding region resulted in partial inhibition of HC-Pro N-terminal cleavage, suggesting that the 35 kd protein may affect the proteolytic event but not in a catalytic role [6].
  • A point mutation affecting an amino acid residue essential for the proteolytic activity of HC-Pro had no effect on N-terminal processing [6].
  • Moreover, high-level expression occurs without viral symptoms and, when HC-Pro is expressed from a mutant transgene, without detrimental developmental phenotypes [7].

Chemical compound and disease context of HC-Pro

  • The first approximately 60 amino acids of the N-terminal part of the potyvirus helper component-proteinase (HC-Pro) include highly conserved residues comprising a Cys-rich region [8].
  • However, when mutations were introduced into the highly conserved "PTK" and "KITC" motifs of HC-Pro, known for their involvement in protein/protein interaction during aphid-mediated transmission of potyvirus, the resulting change of amino acid residue from lysine (K) to glutamic acid (E) in the "KITC" motif had no obvious influence [9].

Biological context of HC-Pro

  • However, it was recently reported that a sequence coding for HCPro is lacking in the genome of Cucumber vein yellowing virus (CVYV), a member of the genus Ipomovirus, the fourth monopartite genus of the family [2].
  • One of the proposed activities of P1 is to assist HCPro, the product that viruses of the genus Potyvirus use to counteract antiviral defense mediated by RNA silencing [2].
  • In the case of PVX-potyviral synergism, we show that the expression of the HC-Pro gene product, but not the RNA sequence itself, is sufficient to induce the increase in PVX pathogenicity and that both P1 and P3 coding sequences are dispensable for this aspect of the synergistic interaction [3].
  • These results indicate that the potyviral P1/HC-Pro region affects a step in disease development that is common to a broad range of virus infections and suggest a mechanism involving transactivation of viral replication [3].
  • In protoplasts, expression of the potyviral P1/HC-Pro region prolongs the accumulation of PVX (-) strand RNA and transactivates expression of a reporter gene from a PVX subgenomic promoter [3].

Anatomical context of HC-Pro


Associations of HC-Pro with chemical compounds

  • The finding that p29-mediated symptom expression is influenced by two cysteine residues that are conserved in the potyvirus-encoded HC-Pro raises the possibility that these related viral-papain-like proteases function in their respective fungal and plant hosts by impacting ancestrally related regulatory pathways [12].
  • Highly purified HC-Pro protein was obtained from plants infected with TEV by using a modified version of the virus that incorporates a histidine tag at the HC-Pro N terminus (hisHC-Pro) [13].
  • To investigate the interrelationships between three of these functions, 25 alanine-scanning mutations affecting clusters of charged residues were introduced into the HC-Pro coding sequence [14].
  • Mutations in the conserved His and two Cys residues within the Cys-rich region have a strong debilitating effect on self-interaction when introduced in the full-length HC-Pro, but not when introduced in the N-terminal fragment [8].
  • To identify the class of proteinase to which HC-Pro belongs, tobacco etch virus (TEV) HC-Pro mutants containing single amino acid substitutions at serine, cysteine, aspartic acid, and histidine positions were synthesized by in vitro transcription and translation and were tested for autoproteolytic activity [15].

Regulatory relationships of HC-Pro

  • In this study, we provide further evidence that P1 enhances the activity of HCPro in members of the genus Potyvirus and show that it is duplicated in the ipomovirus CVYV [2].

Other interactions of HC-Pro

  • The greatest variability occurred in the 5' untranslated region, P1 protein, and NIa-VPg protein, the N-terminal two thirds of HC-Pro, and the C-terminal one third of P3 [16].
  • The potato A potyvirus (PVA)-encoded proteins P1, HC-Pro, P3, CI, VPg, NIaPro, NIb and coat protein (CP) were expressed as 6 x His-tagged recombinant proteins in Escherichia coli and purified to homogeneity [17].
  • The complete genome sequence of one of the recombinant isolates, BOR-3, was determined, as well as some partial sequences in the HC-Pro and P3 genes for additional natural recombinant isolates [18].

Analytical, diagnostic and therapeutic context of HC-Pro

  • Our data from electron microscopy, biochemical analysis, and secondary structure predictions lead us to suggest a model for structure/function relationships in the HC-Pro protein [19].
  • Comparison of projection maps of negatively stained crystals revealed that HC-Pro is composed of two domains separated by a flexible constriction [19].
  • Characterization of these and additional variants derived by site-directed mutagenesis demonstrated that deletion of sequences coding for the HC-Pro N-terminal domain had a negative effect on accumulation of viral RNA and coat protein [20].
  • Electrophoretic mobility-shift assays demonstrated that HC-Pro acts as a sequence non-specific RNA-binding protein and suggest that more than one molecule of protein was bound per molecule of RNA [21].
  • Western blot comparison did not permit attribution of HC-Pro functionality in transmission to its level in the host [22].


  1. Complete nucleotide sequence and genome organization of sweet potato feathery mottle virus (S strain) genomic RNA: the large coding region of the P1 gene. Sakai, J., Mori, M., Morishita, T., Tanaka, M., Hanada, K., Usugi, T., Nishiguchi, M. Arch. Virol. (1997) [Pubmed]
  2. RNA Silencing Suppression by a Second Copy of the P1 Serine Protease of Cucumber Vein Yellowing Ipomovirus, a Member of the Family Potyviridae That Lacks the Cysteine Protease HCPro. Valli, A., Mart??n-Hern??ndez, A.M., L??pez-Moya, J.J., Garc??a, J.A. J. Virol. (2006) [Pubmed]
  3. Plant viral synergism: the potyviral genome encodes a broad-range pathogenicity enhancer that transactivates replication of heterologous viruses. Pruss, G., Ge, X., Shi, X.M., Carrington, J.C., Bowman Vance, V. Plant Cell (1997) [Pubmed]
  4. A counterdefensive strategy of plant viruses: suppression of posttranscriptional gene silencing. Kasschau, K.D., Carrington, J.C. Cell (1998) [Pubmed]
  5. Viral pathogenicity determinants are suppressors of transgene silencing in Nicotiana benthamiana. Brigneti, G., Voinnet, O., Li, W.X., Ji, L.H., Ding, S.W., Baulcombe, D.C. EMBO J. (1998) [Pubmed]
  6. Expression of potyviral polyproteins in transgenic plants reveals three proteolytic activities required for complete processing. Carrington, J.C., Freed, D.D., Oh, C.S. EMBO J. (1990) [Pubmed]
  7. The amplicon-plus system for high-level expression of transgenes in plants. Mallory, A.C., Parks, G., Endres, M.W., Baulcombe, D., Bowman, L.H., Pruss, G.J., Vance, V.B. Nat. Biotechnol. (2002) [Pubmed]
  8. Effect of mutations within the cys-rich region of potyvirus helper component-proteinase on self-interaction. Urcuqui-Inchima, S., Maia, I.G., Drugeon, G., Haenni, A.L., Bernardi, F. J. Gen. Virol. (1999) [Pubmed]
  9. Molecular studies of the synergistic interactions between plum pox virus HC-Pro protein and potato virus X. Yang, S., Ravelonandro, M. Arch. Virol. (2002) [Pubmed]
  10. Autocatalytic processing of the potyvirus helper component proteinase in Escherichia coli and in vitro. Carrington, J.C., Freed, D.D., Sanders, T.C. J. Virol. (1989) [Pubmed]
  11. Ultrastructural localization of nonstructural and coat proteins of 19 potyviruses using antisera to bacterially expressed proteins of plum pox potyvirus. Riedel, D., Lesemann, D.E., Maiss, E. Arch. Virol. (1998) [Pubmed]
  12. Mapping of a hypovirus p29 protease symptom determinant domain with sequence similarity to potyvirus HC-Pro protease. Suzuki, N., Chen, B., Nuss, D.L. J. Virol. (1999) [Pubmed]
  13. Structural analysis of tobacco etch potyvirus HC-pro oligomers involved in aphid transmission. Ruiz-Ferrer, V., Boskovic, J., Alfonso, C., Rivas, G., Llorca, O., López-Abella, D., López-Moya, J.J. J. Virol. (2005) [Pubmed]
  14. Genome amplification and long-distance movement functions associated with the central domain of tobacco etch potyvirus helper component-proteinase. Kasschau, K.D., Cronin, S., Carrington, J.C. Virology (1997) [Pubmed]
  15. Identification of essential residues in potyvirus proteinase HC-Pro by site-directed mutagenesis. Oh, C.S., Carrington, J.C. Virology (1989) [Pubmed]
  16. The complete nucleotide sequence of isolate BYMV-GDD of Bean yellow mosaic virus, and comparison to other potyviruses. Hammond, J., Hammond, R.W. Arch. Virol. (2003) [Pubmed]
  17. VPg, coat protein and five non-structural proteins of potato A potyvirus bind RNA in a sequence-unspecific manner. Merits, A., Guo, D., Saarma, M. J. Gen. Virol. (1998) [Pubmed]
  18. Geographically and temporally distant natural recombinant isolates of Plum pox virus (PPV) are genetically very similar and form a unique PPV subgroup. Glasa, M., Palkovics, L., Komínek, P., Labonne, G., Pittnerová, S., Kúdela, O., Candresse, T., Subr, Z. J. Gen. Virol. (2004) [Pubmed]
  19. Structural characterization of HC-Pro, a plant virus multifunctional protein. Plisson, C., Drucker, M., Blanc, S., German-Retana, S., Le Gall, O., Thomas, D., Bron, P. J. Biol. Chem. (2003) [Pubmed]
  20. Spontaneous mutagenesis of a plant potyvirus genome after insertion of a foreign gene. Dolja, V.V., Herndon, K.L., Pirone, T.P., Carrington, J.C. J. Virol. (1993) [Pubmed]
  21. Nucleic acid-binding properties of a bacterially expressed potato virus Y helper component-proteinase. Maia, I.G., Bernardi, F. J. Gen. Virol. (1996) [Pubmed]
  22. Mutations in the HC-Pro gene of zucchini yellow mosaic potyvirus: effects on aphid transmission and binding to purified virions. Peng, Y.H., Kadoury, D., Gal-On, A., Huet, H., Wang, Y., Raccah, B. J. Gen. Virol. (1998) [Pubmed]
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