作者： Hiroshi Yonemura , Takayuki Imamura , Kenichi Matsubara , Atsushi Miyanohara , Nobuya Ohtomo
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摘要: Thehepatitis Bvirus genome carries thesurface antigen (SAg) gene andan open reading framethatencodes twoSAg-related polypeptides: SAgwitha 55-amino-acid N-terminal extension polypeptide andSAgwitha 174-amino-acid polypeptide. These aretermedmiddle Sandlarge S,respectively. polypeptides or their glycosylated derivatives havebeendetected inDaneparticles, buttheir chemical and biological properties haveremained largely unknownbecause oftheir limited availability. We attempted to produce these proteins inSaccharomyces cerevisiae byplacing thecoding regions underthecontrol ofthe promoter oftheyeastglyceraldehyde-3-phosphate dehydrogenase (GAPDH)gene.Yeastcells carrying middle Scoding sequencesproduced 33,000- and42,000-dalton products, respectively, eachofwhich reacted withanti-S antibody andboundtopolymerized humanserum albumin, inaccordance withtheknown ofpre-S fromparticles inhumansera(K.H.Heermann, U.Goldmann, W.Schwartz, T. Seyffarth, H.Baumgarten, andW.H.Gerlich, J.Virol. 52:396-402, 1984; A.Machida, S.Kishimoto, H. Ohnuma,K.Baba,Y.Ito, H.Miyamoto, G.Funatsu, K.Oda,S.Usuda,S.Togami,T.Nakamura,Y. Miyakawa, andM.Mayumi,Gastroenterology 86:910-918, 1984). Themiddle Spolypeptide isglycosylated andcan beassembled intoparticles whosesizeanddensity are similar tothoseofSAg.However, this was highly susceptible toproteolytic degradation into29,000- and26,000-dalton polypeptides, of whichonlytheformer retained thebinding activity topolymerized albumin. Thelarge Spolypeptides nonglycosylated, relatively stable, anddonotseem toassemble into particles bythemselves. Hepatitis B virus(HBV)isa smallDNA viruswhich infects onlylivers ofhumansandchimpanzees. Theseraof chronic carriers often display 45-nm(Dane) along withsmall particles, bothofwhich carry24,000- and27,000dalton surface (SAg)polypeptides. Thesehavebeen showntobethesame innonglycosylated forms. Inaddition, larger have beendiscovered aswell asinsome small recovered fromeAg-positive patients (7). bindtopolymerized albumin (PHSA) (14). Studies withclonedHBV DNA (3,4,6,23,29)have revealed an aminoacid-coding region located upstreamof andinframewiththeSAg-coding region. Depending upon whichinitiation codonischosen, theproduct isSAgwithan of174or55aminoacids attheN terminus. The sequence starting fromtheinitiation sitefurthest upstream, viz., nucleotide position 2,720 (6), whichencodes SAgwiththe174-amino-acid extension, isdefined as the largeS gene; thesequence thatstartsfromnucleotide 3,077andencodesSAg withthe55-amino-acid asthemiddleS gene.Thelarge Sand middleS geneproducts formwouldbe 42,000 and31,000 daltons, respectively. Forthesakeof clarity, theSAggenethatstarts atnucleotide 28is called themajorS gene. Theextension havebeenclaimed toenhance theimmunogenicity ofSAgineliciting anti-S (7, 16-18, 20),suggesting thattheymay playimportant rolesin theprocessofvirusinfection andtheinduction ofa defensivebodyresponse.However,thelimited availability