Abstract
The polyomavirus enhancer is required in cis for high-level expression of the viral early region and for replication of the viral genome. We introduced multiple mutations in the enhancer which reduced transcription and DNA replication. Polyomaviruses with these mutant enhancers formed very small plaques in whole mouse embryo cells. Revertants of the viral mutants were isolated and characterized. Reversion occurred by any of the following events: restoration of guanosines at nucleotide (nt) 5134 and nt 5140 within the adenovirus 5 E1A enhancer core AGGAAGTGACT; acquisition of an A----G mutation at nt 5258, which is the same mutation that enables polyomavirus to grow in embryonal carcinoma F9 cells; duplication of mutated sequences between nt 5146 and 5292 (including sequences homologous with immunoglobulin G, simian virus 40, and bovine papillomavirus enhancer elements). Reversion restored both the replicative and transcriptional functions of the viruses. Revertants that acquired the F9 mutation at nt 5258 grew at least 20-fold better than the original mutant in whole mouse embryo cells, but replicated only marginally better than the original mutant in 3T6 cells. Viruses with a reversion of the mutation at nt 5140 replicated equally well in both types of cells. Since individual nucleotides in the polyomavirus enhancer simultaneously altered DNA replication and transcription in specific cell types, it is likely that these processes rely upon a common element, such as an enhancer-binding protein.
Full text
PDF









Images in this article
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Banerji J., Olson L., Schaffner W. A lymphocyte-specific cellular enhancer is located downstream of the joining region in immunoglobulin heavy chain genes. Cell. 1983 Jul;33(3):729–740. doi: 10.1016/0092-8674(83)90015-6. [DOI] [PubMed] [Google Scholar]
- Banerji J., Rusconi S., Schaffner W. Expression of a beta-globin gene is enhanced by remote SV40 DNA sequences. Cell. 1981 Dec;27(2 Pt 1):299–308. doi: 10.1016/0092-8674(81)90413-x. [DOI] [PubMed] [Google Scholar]
- Benoist C., Chambon P. In vivo sequence requirements of the SV40 early promotor region. Nature. 1981 Mar 26;290(5804):304–310. doi: 10.1038/290304a0. [DOI] [PubMed] [Google Scholar]
- Berg P. E., Popovic Z., Anderson W. F. Promoter dependence of enhancer activity. Mol Cell Biol. 1984 Aug;4(8):1664–1668. doi: 10.1128/mcb.4.8.1664. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Berger S. L., Folk W. R. Differential activation of RNA polymerase III-transcribed genes by the polyomavirus enhancer and the adenovirus E1A gene products. Nucleic Acids Res. 1985 Feb 25;13(4):1413–1428. doi: 10.1093/nar/13.4.1413. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bryan P. N., Folk W. R. Enhancer sequences responsible for DNase I hypersensitivity in polyomavirus chromatin. Mol Cell Biol. 1986 Jun;6(6):2249–2252. doi: 10.1128/mcb.6.6.2249. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Böhnlein E., Chowdhury K., Gruss P. Functional analysis of the regulatory region of polyoma mutant F9-1 DNA. Nucleic Acids Res. 1985 Jul 11;13(13):4789–4809. doi: 10.1093/nar/13.13.4789. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Böhnlein E., Gruss P. Interaction of distinct nuclear proteins with sequences controlling the expression of polyomavirus early genes. Mol Cell Biol. 1986 May;6(5):1401–1411. doi: 10.1128/mcb.6.5.1401. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Camerini-Otero R. D., Zasloff M. A. Nucleosomal packaging of the thymidine kinase gene of herpes simplex virus transferred into mouse cells: an actively expressed single-copy gene. Proc Natl Acad Sci U S A. 1980 Sep;77(9):5079–5083. doi: 10.1073/pnas.77.9.5079. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Campbell B. A., Villarreal L. P. Lymphoid and other tissue-specific phenotypes of polyomavirus enhancer recombinants: positive and negative combinational effects on enhancer specificity and activity. Mol Cell Biol. 1986 Jun;6(6):2068–2079. doi: 10.1128/mcb.6.6.2068. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Dailey L., Basilico C. Sequences in the polyomavirus DNA regulatory region involved in viral DNA replication and early gene expression. J Virol. 1985 Jun;54(3):739–749. doi: 10.1128/jvi.54.3.739-749.1985. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Davison B. L., Egly J. M., Mulvihill E. R., Chambon P. Formation of stable preinitiation complexes between eukaryotic class B transcription factors and promoter sequences. Nature. 1983 Feb 24;301(5902):680–686. doi: 10.1038/301680a0. [DOI] [PubMed] [Google Scholar]
- Deninger P. L., Esty A., LaPorte P., Hsu H., Friedmann T. The nucleotide sequence and restriction enzyme sites of the polyoma genome. Nucleic Acids Res. 1980 Feb 25;8(4):855–860. [PMC free article] [PubMed] [Google Scholar]
- Farmerie W. G., Folk W. R. Regulation of polyomavirus transcription by large tumor antigen. Proc Natl Acad Sci U S A. 1984 Nov;81(22):6919–6923. doi: 10.1073/pnas.81.22.6919. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fire A., Samuels M., Sharp P. A. Interactions between RNA polymerase II, factors, and template leading to accurate transcription. J Biol Chem. 1984 Feb 25;259(4):2509–2516. [PubMed] [Google Scholar]
- Folk W. R., Hofstetter H. A detailed mutational analysis of the eucaryotic tRNAmet1 gene promoter. Cell. 1983 Jun;33(2):585–593. doi: 10.1016/0092-8674(83)90439-7. [DOI] [PubMed] [Google Scholar]
- Fowler R. G., Degnen G. E., Cox E. C. Mutational specificity of a conditional Escherichia coli mutator, mutD5. Mol Gen Genet. 1974;133(3):179–191. doi: 10.1007/BF00267667. [DOI] [PubMed] [Google Scholar]
- Fowlkes D. M., Shenk T. Transcriptional control regions of the adenovirus VAI RNA gene. Cell. 1980 Nov;22(2 Pt 2):405–413. doi: 10.1016/0092-8674(80)90351-7. [DOI] [PubMed] [Google Scholar]
- Fujimura F. K., Deininger P. L., Friedmann T., Linney E. Mutation near the polyoma DNA replication origin permits productive infection of F9 embryonal carcinoma cells. Cell. 1981 Mar;23(3):809–814. doi: 10.1016/0092-8674(81)90445-1. [DOI] [PubMed] [Google Scholar]
- Fujimura F. K., Linney E. Polyoma mutants that productively infect F9 embryonal carcinoma cells do not rescue wild-type polyoma in F9 cells. Proc Natl Acad Sci U S A. 1982 Mar;79(5):1479–1483. doi: 10.1073/pnas.79.5.1479. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fujimura F. K. Nuclear activity from F9 embryonal carcinoma cells binding specifically to the enhancers of wild-type polyoma virus and PyEC mutant DNAs. Nucleic Acids Res. 1986 Apr 11;14(7):2845–2861. doi: 10.1093/nar/14.7.2845. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ghosh P. K., Reddy V. B., Piatak M., Lebowitz P., Weissman S. M. Determination of RNA sequences by primer directed synthesis and sequencing of their cDNA transcripts. Methods Enzymol. 1980;65(1):580–595. doi: 10.1016/s0076-6879(80)65061-7. [DOI] [PubMed] [Google Scholar]
- Goodbourn S., Zinn K., Maniatis T. Human beta-interferon gene expression is regulated by an inducible enhancer element. Cell. 1985 Jun;41(2):509–520. doi: 10.1016/s0092-8674(85)80024-6. [DOI] [PubMed] [Google Scholar]
- Green H., Goldberg B., Todaro G. J. Differentiated cell types and the regulation of collagen synthesis. Nature. 1966 Nov 5;212(5062):631–633. doi: 10.1038/212631b0. [DOI] [PubMed] [Google Scholar]
- Gruss P., Dhar R., Khoury G. Simian virus 40 tandem repeated sequences as an element of the early promoter. Proc Natl Acad Sci U S A. 1981 Feb;78(2):943–947. doi: 10.1073/pnas.78.2.943. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Guarente L. Yeast promoters: positive and negative elements. Cell. 1984 Apr;36(4):799–800. doi: 10.1016/0092-8674(84)90028-x. [DOI] [PubMed] [Google Scholar]
- Hearing P., Shenk T. The adenovirus type 5 E1A enhancer contains two functionally distinct domains: one is specific for E1A and the other modulates all early units in cis. Cell. 1986 Apr 25;45(2):229–236. doi: 10.1016/0092-8674(86)90387-9. [DOI] [PubMed] [Google Scholar]
- Hearing P., Shenk T. The adenovirus type 5 E1A transcriptional control region contains a duplicated enhancer element. Cell. 1983 Jul;33(3):695–703. doi: 10.1016/0092-8674(83)90012-0. [DOI] [PubMed] [Google Scholar]
- Hen R., Borrelli E., Fromental C., Sassone-Corsi P., Chambon P. A mutated polyoma virus enhancer which is active in undifferentiated embryonal carcinoma cells is not repressed by adenovirus-2 E1A products. Nature. 1986 May 15;321(6067):249–251. doi: 10.1038/321249a0. [DOI] [PubMed] [Google Scholar]
- Herbomel P., Bourachot B., Yaniv M. Two distinct enhancers with different cell specificities coexist in the regulatory region of polyoma. Cell. 1984 Dec;39(3 Pt 2):653–662. doi: 10.1016/0092-8674(84)90472-0. [DOI] [PubMed] [Google Scholar]
- Herbomel P., Saragosti S., Blangy D., Yaniv M. Fine structure of the origin-proximal DNAase I-hypersensitive region in wild-type and EC mutant polyoma. Cell. 1981 Sep;25(3):651–658. doi: 10.1016/0092-8674(81)90172-0. [DOI] [PubMed] [Google Scholar]
- Herr W., Clarke J. The SV40 enhancer is composed of multiple functional elements that can compensate for one another. Cell. 1986 May 9;45(3):461–470. doi: 10.1016/0092-8674(86)90332-6. [DOI] [PubMed] [Google Scholar]
- Herr W., Gluzman Y. Duplications of a mutated simian virus 40 enhancer restore its activity. Nature. 1985 Feb 21;313(6004):711–714. doi: 10.1038/313711a0. [DOI] [PubMed] [Google Scholar]
- Hirt B. Selective extraction of polyoma DNA from infected mouse cell cultures. J Mol Biol. 1967 Jun 14;26(2):365–369. doi: 10.1016/0022-2836(67)90307-5. [DOI] [PubMed] [Google Scholar]
- Jakobovits E. B., Bratosin S., Aloni Y. Formation of a nucleosome-free region in SV40 minichromosomes is dependent upon a restricted segment of DNA. Virology. 1982 Jul 30;120(2):340–348. doi: 10.1016/0042-6822(82)90035-6. [DOI] [PubMed] [Google Scholar]
- Jongstra J., Reudelhuber T. L., Oudet P., Benoist C., Chae C. B., Jeltsch J. M., Mathis D. J., Chambon P. Induction of altered chromatin structures by simian virus 40 enhancer and promoter elements. Nature. 1984 Feb 23;307(5953):708–714. doi: 10.1038/307708a0. [DOI] [PubMed] [Google Scholar]
- Katinka M., Vasseur M., Montreau N., Yaniv M., Blangy D. Polyoma DNA sequences involved in control of viral gene expression in murine embryonal carcinoma cells. Nature. 1981 Apr 23;290(5808):720–722. doi: 10.1038/290720a0. [DOI] [PubMed] [Google Scholar]
- Laimins L. A., Khoury G., Gorman C., Howard B., Gruss P. Host-specific activation of transcription by tandem repeats from simian virus 40 and Moloney murine sarcoma virus. Proc Natl Acad Sci U S A. 1982 Nov;79(21):6453–6457. doi: 10.1073/pnas.79.21.6453. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Leegwater P. A., van der Vliet P. C., Rupp R. A., Nowock J., Sippel A. E. Functional homology between the sequence-specific DNA-binding proteins nuclear factor I from HeLa cells and the TGGCA protein from chicken liver. EMBO J. 1986 Feb;5(2):381–386. doi: 10.1002/j.1460-2075.1986.tb04223.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Li J. J., Peden K. W., Dixon R. A., Kelly T. Functional organization of the simian virus 40 origin of DNA replication. Mol Cell Biol. 1986 Apr;6(4):1117–1128. doi: 10.1128/mcb.6.4.1117. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Linney E., Donerly S. DNA fragments from F9 PyEC mutants increase expression of heterologous genes in transfected F9 cells. Cell. 1983 Dec;35(3 Pt 2):693–699. doi: 10.1016/0092-8674(83)90102-2. [DOI] [PubMed] [Google Scholar]
- Luthman H., Nilsson M. G., Magnusson G. Non-contiguous segments of the polyoma genome required in cis for DNA replication. J Mol Biol. 1982 Nov 15;161(4):533–550. doi: 10.1016/0022-2836(82)90406-5. [DOI] [PubMed] [Google Scholar]
- McCutchan J. H., Pagano J. S. Enchancement of the infectivity of simian virus 40 deoxyribonucleic acid with diethylaminoethyl-dextran. J Natl Cancer Inst. 1968 Aug;41(2):351–357. [PubMed] [Google Scholar]
- Melin F., Pinon H., Reiss C., Kress C., Montreau N., Blangy D. Common features of polyomavirus mutants selected on PCC4 embryonal carcinoma cells. EMBO J. 1985 Jul;4(7):1799–1803. doi: 10.1002/j.1460-2075.1985.tb03853.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Moreau P., Hen R., Wasylyk B., Everett R., Gaub M. P., Chambon P. The SV40 72 base repair repeat has a striking effect on gene expression both in SV40 and other chimeric recombinants. Nucleic Acids Res. 1981 Nov 25;9(22):6047–6068. doi: 10.1093/nar/9.22.6047. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mueller C. R., Mes-Masson A. M., Bouvier M., Hassell J. A. Location of sequences in polyomavirus DNA that are required for early gene expression in vivo and in vitro. Mol Cell Biol. 1984 Dec;4(12):2594–2609. doi: 10.1128/mcb.4.12.2594. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Muller W. J., Mueller C. R., Mes A. M., Hassell J. A. Polyomavirus origin for DNA replication comprises multiple genetic elements. J Virol. 1983 Sep;47(3):586–599. doi: 10.1128/jvi.47.3.586-599.1983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Nowock J., Borgmeyer U., Püschel A. W., Rupp R. A., Sippel A. E. The TGGCA protein binds to the MMTV-LTR, the adenovirus origin of replication, and the BK virus enhancer. Nucleic Acids Res. 1985 Mar 25;13(6):2045–2061. doi: 10.1093/nar/13.6.2045. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ostapchuk P., Diffley J. F., Bruder J. T., Stillman B., Levine A. J., Hearing P. Interaction of a nuclear factor with the polyomavirus enhancer region. Proc Natl Acad Sci U S A. 1986 Nov;83(22):8550–8554. doi: 10.1073/pnas.83.22.8550. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Parker B. A., Stark G. R. Regulation of simian virus 40 transcription: sensitive analysis of the RNA species present early in infections by virus or viral DNA. J Virol. 1979 Aug;31(2):360–369. doi: 10.1128/jvi.31.2.360-369.1979. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Picard D. Viral and cellular transcription enhancers. Oxf Surv Eukaryot Genes. 1985;2:24–48. [PubMed] [Google Scholar]
- Piette J., Kryszke M. H., Yaniv M. Specific interaction of cellular factors with the B enhancer of polyoma virus. EMBO J. 1985 Oct;4(10):2675–2685. doi: 10.1002/j.1460-2075.1985.tb03987.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Robbins P. D., Rio D. C., Botchan M. R. trans Activation of the simian virus 40 enhancer. Mol Cell Biol. 1986 Apr;6(4):1283–1295. doi: 10.1128/mcb.6.4.1283. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Rothwell V. M., Folk W. R. Comparison of the DNA sequence of the Crawford small-plaque variant of polyomavirus with those of polyomaviruses A2 and strain 3. J Virol. 1983 Nov;48(2):472–480. doi: 10.1128/jvi.48.2.472-480.1983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ruley H. E., Fried M. Sequence repeats in a polyoma virus DNA region important for gene expression. J Virol. 1983 Jul;47(1):233–237. doi: 10.1128/jvi.47.1.233-237.1983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Saragosti S., Moyne G., Yaniv M. Absence of nucleosomes in a fraction of SV40 chromatin between the origin of replication and the region coding for the late leader RNA. Cell. 1980 May;20(1):65–73. doi: 10.1016/0092-8674(80)90235-4. [DOI] [PubMed] [Google Scholar]
- Sawadogo M., Roeder R. G. Factors involved in specific transcription by human RNA polymerase II: analysis by a rapid and quantitative in vitro assay. Proc Natl Acad Sci U S A. 1985 Jul;82(13):4394–4398. doi: 10.1073/pnas.82.13.4394. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sekikawa K., Levine A. J. Isolation and characterization of polyoma host range mutants that replicate in nullipotential embryonal carcinoma cells. Proc Natl Acad Sci U S A. 1981 Feb;78(2):1100–1104. doi: 10.1073/pnas.78.2.1100. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sergeant A., Bohmann D., Zentgraf H., Weiher H., Keller W. A transcription enhancer acts in vitro over distances of hundreds of base-pairs on both circular and linear templates but not on chromatin-reconstituted DNA. J Mol Biol. 1984 Dec 15;180(3):577–600. doi: 10.1016/0022-2836(84)90028-7. [DOI] [PubMed] [Google Scholar]
- Shortle D., Nathans D. Local mutagenesis: a method for generating viral mutants with base substitutions in preselected regions of the viral genome. Proc Natl Acad Sci U S A. 1978 May;75(5):2170–2174. doi: 10.1073/pnas.75.5.2170. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Soeda E., Arrand J. R., Smolar N., Walsh J. E., Griffin B. E. Coding potential and regulatory signals of the polyoma virus genome. Nature. 1980 Jan 31;283(5746):445–453. doi: 10.1038/283445a0. [DOI] [PubMed] [Google Scholar]
- Stillman B., Gerard R. D., Guggenheimer R. A., Gluzman Y. T antigen and template requirements for SV40 DNA replication in vitro. EMBO J. 1985 Nov;4(11):2933–2939. doi: 10.1002/j.1460-2075.1985.tb04026.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Swartzendruber D. E., Lehman J. M. Neoplastic differentiation: interaction of simian virus 40 and polyoma virus with murine teratocarcinoma cells in vitro. J Cell Physiol. 1975 Apr;85(2 Pt 1):179–187. doi: 10.1002/jcp.1040850204. [DOI] [PubMed] [Google Scholar]
- Tanaka K., Chowdhury K., Chang K. S., Israel M., Ito Y. Isolation and characterization of polyoma virus mutants which grow in murine embryonal carcinoma and trophoblast cells. EMBO J. 1982;1(12):1521–1527. doi: 10.1002/j.1460-2075.1982.tb01349.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Theisen M., Stief A., Sippel A. E. The lysozyme enhancer: cell-specific activation of the chicken lysozyme gene by a far-upstream DNA element. EMBO J. 1986 Apr;5(4):719–724. doi: 10.1002/j.1460-2075.1986.tb04273.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Tyndall C., La Mantia G., Thacker C. M., Favaloro J., Kamen R. A region of the polyoma virus genome between the replication origin and late protein coding sequences is required in cis for both early gene expression and viral DNA replication. Nucleic Acids Res. 1981 Dec 11;9(23):6231–6250. doi: 10.1093/nar/9.23.6231. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Veldman G. M., Lupton S., Kamen R. Polyomavirus enhancer contains multiple redundant sequence elements that activate both DNA replication and gene expression. Mol Cell Biol. 1985 Apr;5(4):649–658. doi: 10.1128/mcb.5.4.649. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wake C. T., Gudewicz T., Porter T., White A., Wilson J. H. How damaged is the biologically active subpopulation of transfected DNA? Mol Cell Biol. 1984 Mar;4(3):387–398. doi: 10.1128/mcb.4.3.387. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weaver R. F., Weissmann C. Mapping of RNA by a modification of the Berk-Sharp procedure: the 5' termini of 15 S beta-globin mRNA precursor and mature 10 s beta-globin mRNA have identical map coordinates. Nucleic Acids Res. 1979 Nov 10;7(5):1175–1193. doi: 10.1093/nar/7.5.1175. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weiher H., Botchan M. R. An enhancer sequence from bovine papilloma virus DNA consists of two essential regions. Nucleic Acids Res. 1984 Mar 26;12(6):2901–2916. doi: 10.1093/nar/12.6.2901. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weiher H., König M., Gruss P. Multiple point mutations affecting the simian virus 40 enhancer. Science. 1983 Feb 11;219(4585):626–631. doi: 10.1126/science.6297005. [DOI] [PubMed] [Google Scholar]
- Wildeman A. G., Sassone-Corsi P., Grundström T., Zenke M., Chambon P. Stimulation of in vitro transcription from the SV40 early promoter by the enhancer involves a specific trans-acting factor. EMBO J. 1984 Dec 20;3(13):3129–3133. doi: 10.1002/j.1460-2075.1984.tb02269.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wobbe C. R., Dean F. B., Murakami Y., Weissbach L., Hurwitz J. Simian virus 40 DNA replication in vitro: study of events preceding elongation of chains. Proc Natl Acad Sci U S A. 1986 Jul;83(13):4612–4616. doi: 10.1073/pnas.83.13.4612. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zenke M., Grundström T., Matthes H., Wintzerith M., Schatz C., Wildeman A., Chambon P. Multiple sequence motifs are involved in SV40 enhancer function. EMBO J. 1986 Feb;5(2):387–397. doi: 10.1002/j.1460-2075.1986.tb04224.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- de Villiers J., Olson L., Tyndall C., Schaffner W. Transcriptional 'enhancers' from SV40 and polyoma virus show a cell type preference. Nucleic Acids Res. 1982 Dec 20;10(24):7965–7976. doi: 10.1093/nar/10.24.7965. [DOI] [PMC free article] [PubMed] [Google Scholar]
- de Villiers J., Schaffner W. A small segment of polyoma virus DNA enhances the expression of a cloned beta-globin gene over a distance of 1400 base pairs. Nucleic Acids Res. 1981 Dec 11;9(23):6251–6264. doi: 10.1093/nar/9.23.6251. [DOI] [PMC free article] [PubMed] [Google Scholar]
- de Villiers J., Schaffner W., Tyndall C., Lupton S., Kamen R. Polyoma virus DNA replication requires an enhancer. Nature. 1984 Nov 15;312(5991):242–246. doi: 10.1038/312242a0. [DOI] [PubMed] [Google Scholar]
- van der Eb A. J., Graham F. L. Assay of transforming activity of tumor virus DNA. Methods Enzymol. 1980;65(1):826–839. doi: 10.1016/s0076-6879(80)65077-0. [DOI] [PubMed] [Google Scholar]