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Gene Review

bel1  -  Bel1

Human spumaretrovirus

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Disease relevance of bel1

  • One of the characteristic features of spumavirus transcription is the existence of singly spliced bel1 and bel2 mRNAs that alternatively are multiply spliced, thereby generating a complexity comparable to, but different from, that of lentiviruses and from that of other known retroviruses [1].
  • Bel-specific transcripts that initiate at the internal transcriptional start site at nt 9196 were identified in HSRV-infected cells by primer extension and S1 nuclease analysis, and the intragenic promoter was shown to be constitutively activated by Bel-1 in the HSRV provirus [2].
  • High-level trans-activation by bel1 was specific for the HSRV LTR, as relatively minor positive and negative regulatory effects were observed on HIV-1 LTR and RSV LTR expression, respectively, whereas HTLV-1 LTR activity remained unaffected [3].
  • In the region of the HIV-1 LTR that is necessary for the bel1-mediated transactivation, we have found a sequence which is conserved between HIV-1 and HFV [4].
  • Comparison between the viral sequences suggests that the 3'-orf and bel1 gene product of HSRV could serve similar functions to those in HIV-2 [5].

High impact information on bel1


Chemical compound and disease context of bel1


Biological context of bel1

  • Deletion mutagenesis of the transcriptional HSRV-specific trans-activator bel 1 and the bet genes completely abolished the infectivity of the pHSRV13 clone [10].
  • Distinct cis-acting regions in U3 regulate trans-activation of the human spumaretrovirus long terminal repeat by the viral bel1 gene product [3].
  • The human spumaretrovirus (HSRV) genome contains, in addition to coding information for the structural proteins, open reading frames (ORFs) for at least three additional genes termed bel1, bel2 and bel3 [3].
  • The observation that the multiple distinct elements in the HFV LTR are the targets for bel1 transactivation is different from observations with other human retroviral systems [11].
  • In addition, the region between -466 and -498 was identified as responsible for the downregulation of gene expression directed by BREa, which requires its upstream sequence element to act as a bel1-dependent enhancer element in a heterologous promoter [11].

Anatomical context of bel1

  • In reporter-based transient expression assays in COS cells utilizing the bacterial CAT gene linked to HSRV LTR sequences between -710 and +309 with respect to the transcriptional initiation site, co-expression of the bel1 gene product alone caused an over 100 to 300-fold increase in the level of LTR activity [3].
  • The Bel-1 trans activator is shown to function effectively in cell lines derived from human, simian, murine, and avian sources [12].
  • Mutational analysis has identified a small, discrete activation domain within Bel-1 that is highly active in both higher and lower eukaryotic cells [13].

Associations of bel1 with chemical compounds


Analytical, diagnostic and therapeutic context of bel1

  • By PCR, we have detected HFV sequences with a non-random deletion in the bel1 transactivator gene in other autoimmune conditions [6].
  • The bel1 and Pol sequences of HFV were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) in plasma and by PCR in peripheral blood mononuclear cells (PBMC) from patients with SLE, RA, and PSS [14].
  • Expression of the human cyclin-dependent protein kinase inhibitor p57(Kip2) gene was previously shown to be specifically and strongly activated by the retroviral trans-activator Bel1 of human foamy virus by means of expression profiling, Northern, and Western blot analysis [8].
  • By using site-directed mutagenesis, we have identified distinct regions of Bel1 essential for HSRV LTR activation [15].
  • By DNA footprinting and gel retardation analysis, we demonstrate that Bel-1 can specifically bind to discrete sites in both the LTR and Int promoter elements in vitro [16].


  1. Analysis of splicing patterns of human spumaretrovirus by polymerase chain reaction reveals complex RNA structures. Muranyi, W., Flügel, R.M. J. Virol. (1991) [Pubmed]
  2. Human foamy virus genome possesses an internal, Bel-1-dependent and functional promoter. Löchelt, M., Muranyi, W., Flügel, R.M. Proc. Natl. Acad. Sci. U.S.A. (1993) [Pubmed]
  3. Distinct cis-acting regions in U3 regulate trans-activation of the human spumaretrovirus long terminal repeat by the viral bel1 gene product. Venkatesh, L.K., Theodorakis, P.A., Chinnadurai, G. Nucleic Acids Res. (1991) [Pubmed]
  4. Transactivation of human immunodeficiency virus type 1 long terminal repeat-directed gene expression by the human foamy virus bel1 protein requires a specific DNA sequence. Lee, A.H., Lee, K.J., Kim, S., Sung, Y.C. J. Virol. (1992) [Pubmed]
  5. The 3'-orf protein of human immunodeficiency virus 2 shows sequence homology with the bel3 gene of the human spumaretrovirus. Maurer, B., Flügel, R.M. FEBS Lett. (1987) [Pubmed]
  6. A defective human foamy provirus generated by pregenome splicing. Saïb, A., Périès, J., de Thé, H. EMBO J. (1993) [Pubmed]
  7. Human foamy virus: an underestimated neuropathogen? Aguzzi, A., Bothe, K., Wagner, E.F., Rethwilm, A., Horak, I. Brain Pathol. (1992) [Pubmed]
  8. Identification and functional characterization of an intragenic DNA binding site for the spumaretroviral trans-activator in the human p57Kip2 gene. Kido, K., Doerks, A., Lochelt, M., Flügel, R.M. J. Biol. Chem. (2002) [Pubmed]
  9. BEL-1 transactivator responsive sequences in the long terminal repeat of human foamy virus. Erlwein, O., Rethwilm, A. Virology (1993) [Pubmed]
  10. Construction of an infectious DNA clone of the full-length human spumaretrovirus genome and mutagenesis of the bel 1 gene. Löchelt, M., Zentgraf, H., Flügel, R.M. Virology (1991) [Pubmed]
  11. Multiple positive and negative cis-acting elements that mediate transactivation by bel1 in the long terminal repeat of human foamy virus. Lee, K.J., Lee, A.H., Sung, Y.C. J. Virol. (1993) [Pubmed]
  12. Characterization of the transcriptional trans activator of human foamy retrovirus. Keller, A., Partin, K.M., Löchelt, M., Bannert, H., Flügel, R.M., Cullen, B.R. J. Virol. (1991) [Pubmed]
  13. Genetic analysis indicates that the human foamy virus Bel-1 protein contains a transcription activation domain of the acidic class. Blair, W.S., Bogerd, H., Cullen, B.R. J. Virol. (1994) [Pubmed]
  14. Human foamy virus bel1 sequence in patients with autoimmune rheumatic diseases. Sun, K.H., Lin, H.Y., Chen, L.W., Tai, H.Y., Lin, M.L., Feng, C.K., Sung, J.S., Liu, H.F., Liu, W.T. Clin. Rheumatol. (2006) [Pubmed]
  15. Functional dissection of the human spumaretrovirus transactivator identifies distinct classes of dominant-negative mutants. Venkatesh, L.K., Yang, C., Theodorakis, P.A., Chinnadurai, G. J. Virol. (1993) [Pubmed]
  16. The human foamy virus Bel-1 transcription factor is a sequence-specific DNA binding protein. He, F., Blair, W.S., Fukushima, J., Cullen, B.R. J. Virol. (1996) [Pubmed]
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