Genomic organization is a well conserved feature among papillomaviruses. Taking HPV-16 as a model, we can distinguish the three main regions (early, late and the long control region)of all papillomaviruses. In the early region (E) resides the transformation and immortalization potential of HPVs and consists of a number of  regulatory genes for viral transcription and replication and cell cycle control. The late region (L) codes for the two capsid genes and the long control region (LCR) contains all the cis-regulatory elements necessary for HPV transcription including the early promoter and the origin of replication (ori). Click on the sensitive map to the different HPV genes.

E6 and E7 Genes
 

     E6 and E7 genes code for small nuclear protein products of about 16-19 and 10-14 kD, respectively (1,2). Both genes are found and expressed in all HPV-containing cells(3,4). The E6 product from high-risk HPV-16 and 18 interacts with the antioncogenic regulator p53 and the ubiquitin degradation pathway protein E6AP, leading to the degradation of the p53 protein (5-7). Low-risk HPV types 6 and 11 E6 protein does not induce p53 degradation corerrelating with their weak transformation potential(8-10). Absence of functional p53 protein makes the cell highly susceptible to DNA damage and prevents the activation of p53-mediated apoptosis. It is noteworthy that most HPV-positive tumors have wild-type p53 whereas HPV-negative tumors contain mutant p53 (11-13).
     HPV-16 E6 gene has two alternative splicing sites resulting in the production of two additional protein products named E6*I and E6*II. However, only the full-length E6 has the capacity to interact with p53 and thus is the only one with clinical relevance.  The E6 protein contains four Cys-X-X-Cys motifs forming zinc-binding structures similar to those present in several transcription factors (14,15). Nevertheless, a role for E6 in HPV transcription has not been clearly established .
     HPV-16 E7 gene is expressed as a part of a polycistronic early transcript which also contains E6. As both transforming genes are expressed from the same mRNA, this transcript has become a target for gene inhibition therapies. The E7 protein product contains two Cys-X-X-Cys motifs which are able to bind zinc and presents transforming and transcriptional regulatory functions similar to E1A protein from Adenovirus and the Large T antigen from SV40 (15-17). Although E7 is able to solely transform and immortilize cells in vitro (18), it requires of E6 to fully display HPV transformation and immortalization capabilities (19,20). As E1A ans Large T, E7 controls the cell cycle by interacting with the antioncogenic regulator P105 RB (21,22) and other RB-associated proteins such as P107 and P130, displacing the E2F transcription factor (23). This results in the unregulated activation of the cell cycle in the infected cell (24-26).

E1 gene
 

    The E1 gene encodes the largest HPV protein (68-76 kD). E1 is a nuclear phosphoprotein essential for HPV replication that interacts with E2 and bind with high affinity the origin of replication (ori) located within the LCR (27,28). The functions of E1 are associated with DNA replication and consist of ATP-binding helicase activity and physical interaction with numerous components of the cellular DNA replication machinery (i.e., DNA polymerase alpha and primase) (29-31).

E2 gene
 

     The E2 gene encodes a 48 kD highly phosphorylated protein. In HPVs, E2 regulates viral DNA transcription and replication through interaction with the partially palindromic sequences, 5'-ACCN6G[GT]T-3' located within the LCR (32-36). In HPV-16 and HPV-18 there are four of such sites and the E2 protein suppresses the promoter from which E6 and E7 (transforming) proteins are transcribed. When HPV-16 integrates into the host-cell chromosome, the integrity of the E1 and E2 genes is disrupted, with the result that repression of E6 and E7 may be affected (37-39). This is because in most genital HPVs there are two E2 binding sites located in close proximity to the early promoter TATA box, displacing basal transcription factors and thus inhibiting initiation . In contrast, cutaneous HPVs and animal papillomaviruses have their E2 binding sites located more distantly from the TATA box, resulting in that E2 is able to activate transcription (40-42). The E2 protein contains three different domains: the carboxy-end DNA binding domain and the amino-end with transcriptional activation capabilities separated by a proline rich "hinge" domain (43). Interaction of E2 with its DNA target site is made directly with the G nucleotides present in the E2 binding site, through a mechanism that requires E2 dimerization. A detailed crystal structure of E2 DNA binding domain/DNA is shown below (44-47).

E5 gene
 

     The E5 gene encodes a small hydrophobic protein typically found in membrane compartments including the Golgi (48-51). In BPV-1, it is a 7 kD cell-transforming protein, which appears to exert its effect through stimulation of growth factor receptor signal transduction pathways (52). It binds to and activates the PDGF receptor (platelet-derived growth factor), and also binds the 16kDa pore protein (ATPase subunit) and a 120 kDa adaptin-related protein of fibroblasts (53-58). It is one of the more poorly conserved open reading frames among the papillomaviruses.

L1 and L2 genes
 

     The L1 gene encodes the 56-60 kD major capsid protein. L1, the most antigenic of papillomavirus proteins, is weakly phosphorylated and does not bind DNA (59,60). It can be glycosylated and cross-linked through disulfides, but the implications of these changes are unclear. (Glycosylated forms have not been reported in virions). It is relatively well-conserved among all papillomaviruses. L1 has self-assembly capacity and is the overwhelmingly predominant molecule in the viral capsid (61,62).The L2 gene encodes the 49-60 kD minor capsid protein, which is highly phosphorylated and binds DNA. L2 migrates in a gel as if it were a 73 kD protein. Unlike L1, L2 does not self-assemble nor does it link to itself (63).

Long Control Region (LCR)
 

     The Long Control Region (LCR) (sometimes referred to as upstream regulatory region (URR) or noncoding region). Operationally defined as the region from the termination of the L1 gene to the first methionine of the E6 gene (Some authors use the beginning of the E6 gene). The LCR is the less conserved region among papillomaviruses. It contains the early promoter and various transcriptional regulatory motifs including those from the AP-1 family, YY1, NF-1/CTF, Octa, TEF-2 and Sp1 (35,64-70)and the binding sites for the viral coded E2 regulator. The origin of replication (ori) is also located within the LCR, normally centered between two E2 binding sites(27).

Reference List

1.  Greenfield, I., Nickerson, J., Penman, S. & Stanley, M. (1991)  Proc.Natl.Acad.Sci.U.S.A.  88, 11217-11221.
 2.  Fujikawa, K., Furuse, M., Uwabe, K.-I., Maki, H. & Yoshie, O. (1994)  Virology  204, 789-793.
 3.  Smotkin, D. & Wettstein, F.O. (1986)  Proc.Natl.Acad.Sci.U.S.A.  83, 4680-4684.
 4.  Androphy, E.J., Hubbert, N.L., Schiller, J.T. & Lowy, D.R. (1987)  EMBO J.  6, 989-992.
 5.  Werness, B.A., Levine, A.J. & Howley, P.M. (1990)  Science  248, 76-79.
 6.  Huibregtse, J.M., Scheffner, M. & Howley, P.M. (1991)  EMBO J.  10, 4129-4135.
 7.  Hubbert, N.L., Sedman, S.A. & Schiller, J.T. (1992)  J.Virol.  66, 6237-6241.
 8.  Gage, J.R., Meyers, C. & Wettstein, F.O. (1990)  J.Virol.  64, 723-730.
 9.  Barbosa, M.S., Vass, W.C., Lowy, D.R. & Schiller, J.T. (1991)  J.Virol.  65, 292-298.

Back to Top
Back to LTG Home Page

10.  Halbert, C.L., Demers, G.W. & Galloway, D.A. (1992)  J.Virol.  66, 2125-2134.
 11.  Crook, T., Wrede, D. & Vousden, K.H. (1991)  Oncogene  6, 873-875.
 12.  Crook, T., Wrede, D., Tidy, J., Scholefield, J., Crawford, L. & Vousden, K.H. (1991)  Oncogene   6, 1251-1257.
 13.  Crook, T., Wrede, D., Tidy, J.A., Mason, W.P., Evans, D.J. & Vousden, K.H. (1992)  Lancet  339, 1070-1073.
 14.  Grossman, S.R. & Laimins, L.A. (1989)  Oncogene  4, 1089-1093.
 15.  Barbosa, M.S., Lowy, D.R. & Schiller, J.T. (1989)  J.Virol.  63, 1404-1407.
 16.  Phelps, W.C., Yee, C.L., Munger, K. & Howley, P.M. (1988)  Cell  53, 539-547.
 17.  Phelps, W.C., Bagchi, S., Barnes, J.A., Raychaudhuri, P., Kraus, V., Munger, K., Howley, P.M. & Nevins, J.R. (1991)  J.Virol.  65, 6922-6930.
 18.  Halbert, C.L., Demers, G.W. & Galloway, D.A. (1991)  J.Virol.  65, 473-478.
 19.  Barbosa, M.S. & Schlegel, R. (1989)  Oncogene  4, 1529-1532.

Back to Top
Back to LTG Home Page

20.  Sedman, S.A., Barbosa, M.S., Vass, W.C., Hubbert, N.L., Haas, J.A., Lowy, D.R. & Schiller, J.T. (1991)  J.Virol.  65, 4860-4866.
 21.  Dyson, N., Howley, P.M., Munger, K. & Harlow, E. (1989)  Science  243, 934-937.
 22.  Munger, K., Phelps, W.C., Bubb, V., Howley, P.M. & Schlegel, R. (1989)  J.Virol.  63 , 4417-4421.
 23.  Chellappan, S., Kraus, V.B., Kroger, B., Munger, K., Howley, P.M., Phelps, W.C. & Nevins, J.R. (1992)  Proc.Natl.Acad.Sci.U.S.A. 89, 4549-4553.
 24.  Morozov, A., Shiyanov, P., Barr, E., Leiden, J.M. & Raychaudhuri, P. (1997)  J.Virol.  71, 3451-3457.
 25.  Ruesch, M.N. & Laimins, L.A. (1997)  J.Virol.  71, 5570-5578.
 26.  Broudy, V.C., Lin, N.L., Buhring, H.J., Komatsu, N. & Kavanagh, T.J. (1998)  Blood  91, 898-906.
 27.  Chiang, C.M., Dong, G., Broker, T.R. & Chow, L.T. (1992)  J.Virol.  66, 5224-5231.
 28.  Kuo, S.R., Liu, J.S., Broker, T.R. & Chow, L.T. (1994)  J.Biol.Chem.  269, 24058-24065.
 29.  Conger, K.L., Liu, J.S., Kuo, S.R., Chow, L.T. & Wang, T.S. (1999)  J.Biol.Chem.  274, 2696-2705.

Back to Top
Back to LTG Home Page

30.  Liu, J.S., Kuo, S.R., Broker, T.R. & Chow, L.T. (1995)  J.Biol.Chem.  270, 27283-27291.
 31.  Swindle, C.S., Zou, N., Van Tine, B.A., Shaw, G.M., Engler, J.A. & Chow, L.T. (1999)  J.Virol.   73, 1001-1009.
 32.  Spalholz, B.A., Yang, Y.C. & Howley, P.M. (1985)  Cell  42, 183-191.
 33.  Phelps, W.C. & Howley, P.M. (1987)  J.Virol.  61, 1630-1638.
 34.  McBride, A.A., Schlegel, R. & Howley, P.M. (1988)  EMBO J.  7, 533-539.
 35.  Thierry, F. & Yaniv, M. (1987)  EMBO J.  6, 3391-3397.
 36.  Bernard, B.A., Bailly, C., Lenoir, M.C., Darmon, M., Thierry, F. & Yaniv, M. (1989)  J.Virol.  63, 4317-4324.
 37.  Schwarz, E., Freese, U.K., Gissmann, L., Mayer, W., Roggenbuck, B., Stremlau, A. & Zur Hausen, H. (1985)  Nature  314, 111-114.
 38.  Baker, C.C., Phelps, W.C., Lindgren, V., Braun, M.J., Gonda, M.A. & Howley, P.M. (1987)  J.Virol.  61, 962-971.
 39.  Pater, M.M. & Pater, A. (1985)  Virology  145, 313-318.

Back to Top
Back to LTG Home Page

40.  Demeret, C., Yaniv, M. & Thierry, F. (1994)  J.Virol.  68, 7075-7082.
 41.  Ham, J., Steger, G. & Yaniv, M. (1994)  EMBO J.  13, 147-157.
 42.  Steger, G., Ham, J. & Yaniv, M. (1996)  Methods Enzymol.  274, 173-185.
 43.  Giri, I. & Yaniv, M. (1988)  EMBO J.  7, 2823-2829.
 44.  Thain, A., Webster, K., Emery, D., Clarke, A.R. & Gaston, K. (1997)  J.Biol.Chem.  272, 8236-8242.
 45.  Hegde, R.S., Grossman, S.R., Laimins, L.A. & Sigler, P.B. (1992)  Nature  359, 505-512.
 46.  Kenworthy, A.K. & Edidin, M. (1998)  J.Cell Biol.  142, 69-84.
 47.  Liang, H., Petros, A.M., Meadows, R.P., Yoon, H.S., Egan, D.A., Walter, K., Holzman, T.F., Robins, T. & Fesik, S.W. (1996)  Biochemistry  35, 2095-2103.
 48.  Schlegel, R., Wade-Glass, M., Rabson, M.S. & Yang, Y.C. (1986)  Science  233, 464-467.
 49.  Bubb, V., McCance, D.J. & Schlegel, R. (1988)  Virology  163, 243-246.

Back to Top
Back to LTG Home Page

50.  Horwitz, B.H., Burkhardt, A.L., Schlegel, R. & DiMaio, D. (1988)  Mol.Cell Biol.  8, 4071-4078.
 51.  Burkhardt, A., Willingham, M., Gay, C., Jeang, K.T. & Schlegel, R. (1989)  Virology  170, 334-339.
 52.  Martin, P., Vass, W.C., Schiller, J.T., Lowy, D.R. & Velu, T.J. (1989)  Cell  59, 21-32.
 53.  Goldstein, D.J. & Schlegel, R. (1990)  EMBO J.  9, 137-145.
 54.  Goldstein, D.J., Finbow, M.E., Andresson, T., McLean, P., Smith, K., Bubb, V. & Schlegel, R. (1991)  Nature  352, 347-349.
 55.  Goldstein, D.J., Andresson, T., Sparkowski, J.J. & Schlegel, R. (1992)  EMBO J.  11, 4851-4859.
 56.  Cohen, B.D., Lowy, D.R. & Schiller, J.T. (1993)  Mol.Cell Biol.  13, 6462-6468.
 57.  Cohen, B.D., Goldstein, D.J., Rutledge, L., Vass, W.C., Lowy, D.R., Schlegel, R. & Schiller, J.T. (1993)  J.Virol.  67, 5303-5311.
 58.  Conrad, M., Bubb, V.J. & Schlegel, R. (1993)  J.Virol.  67, 6170-6178.
 59.  Kirnbauer, R., Booy, F., Cheng, N., Lowy, D.R. & Schiller, J.T. (1992)  Proc.Natl.Acad.Sci.U.S.A.  89, 12180-12184.

Back to Top
Back to LTG Home Page

60.  Kirnbauer, R., Taub, J., Greenstone, H., Roden, R., Durst, M., Gissmann, L., Lowy, D.R. & Schiller, J.T. (1993)  J.Virol.  67, 6929-6936.
 61.  Christensen, N.D., Hopfl, R., DiAngelo, S.L., Cladel, N.M., Patrick, S.D., Welsh, P.A., Budgeon, L.R., Reed, C.A. & Kreider, J.W. (1994)  J.Gen.Virol.  75, 2271-2276.
 62.  Le Cann, P., Coursaget, P., Iochmann, S. & Touze, A. (1994)  FEMS Microbiol.Lett.  117, 269-274.
 63.  Day, P.M., Roden, R.B., Lowy, D.R. & Schiller, J.T. (1998)  J.Virol.  72, 142-150.
 64.  Garcia-Carranca, A., Thierry, F. & Yaniv, M. (1988)  J.Virol.  62, 4321-4330.
 65.  Chong, T., Chan, W.K. & Bernard, H.U. (1990)  Nucleic.Acids.Res.  18, 465-470.
 66.  Chong, T., Apt, D., Gloss, B., Isa, M. & Bernard, H.U. (1991)  J.Virol.  65, 5933-5943.
 67.  Thierry, F., Spyrou, G., Yaniv, M. & Howley, P. (1992)  J.Virol.  66, 3740-3748.
 68.  Apt, D., Chong, T., Liu, Y. & Bernard, H.U. (1993)  J.Virol.  67, 4455-4463.
 69.  Tan, S.H., Leong, L.E., Walker, P.A. & Bernard, H.U. (1994)  J.Virol.  68, 6411-6420.
70.  O'Connor, M.J., Tan, S.H., Tan, C.H. & Bernard, H.U. (1996)  J.Virol.  70, 6529-6539.

Back to Top

Back to LTG Home Page