Sequence of the nucleoprotein gene from a virulent British field isolate of transmissible gastroenteritis virus and its expression in Saccharomyces cerevisiae

Subgenomic mRNA from a virulent isolate of porcine transmissible gastroenteritis virus (TGEV) was used to produce cDNA which was sequenced. Two non-overlapping open reading frames (ORFs) were identified. The largest, encoding a polypeptide of 382 amino acids (relative molecular mass (Mr) 43,483), was shown to be the viral nucleoprotein gene. The second ORF, found 3' to the larger ORF, encodes a polypeptide of 78 amino acids (Mr 9068) which has yet to be assigned to a viral product. The nucleoprotein gene was expressed in yeast cells under the control of two types of yeast promoters: the constitutive PGK promoter, and the inducible GAL1 promoter. Yeast cells containing recombinant plasmids, with the nucleoprotein gene in the correct orientation, produced a polypeptide of Mr 47,000, identical to the viral product, that reacted with a specific monoclonal antibody.     

Expression of a human cytomegalovirus gp58 antigenic domain fused to the hepatitis B virus nucleocapsid protein

Abstract Hepatitis B virus core antigen (HBcAg) has been used as a carrier for expression and presentation of a variety of heterologous viral epitopes in particulate form. The aim of this study was to produce hybrid antigens comprising HBcAg and an immunogenic epitope of human cytomegalovirus (HCMV). A direct comparison was made of amino and carboxyl terminal fusions in order to investigate the influence of position of the foreign epitope on hybrid core particle formation, antigenicity and immunogenicity. HCMV DNA encoding a neutralising epitope of the surface glycoprotein gp58 was either inserted at the amino terminus or fused to the truncated carboxyl terminus of HBcAg and expressed in Escherichia coli . The carboxyl terminal fusion (HBc_3–144-HCMV) was expressed at high levels and assembled into core like particles resembling native HBcAg. Protein with a similar fusion at the amino terminus (HCMV-HBc_1–183) could not be purified or characterised immunologically, although it formed core like particles. HBc_3–144-HCMV displayed HBc antigenicity but HCMV antigenicity could not be detected by radioimmunoassay or western blotting using anti-HCMV monoclonal antibody 7–17 or an anti-HCMV human polyclonal antiserum. Following immunisation of rabbits with HBc_3–144-HCMV, a high titre of anti-HBc specific antibody was produced along with lower titres of HCMV/gp58 specific antibody.     

Immunochemistry and polypeptide composition of hepatitis B core antigen (HBc Ag).

Core particles were isolated from a nuclear extract of a hepatitis B-infected liver labeled with 125I by using chloramine-T and further purified by rate zonal sedimentation on sucrose gradients. Iodinated HBcAg was used as a ligand in a sensitive double-antibody radioimmunoprecipitation (RIP) assay for antibody to HBcAg. The specificity of the RIP reaction was evaluated using defined anti-HBc sera and paired sera from six well-documented cases of hepatitis B infection. The polypeptide composition of the iodinated antigen was examined by SDS-polyacrylamide gel electrophoresis of solubilized complexes of 125I-HBcAg and anti-HBc. Two major polypeptides with apparent m.w. of 17,000 and 35,000 daltons were observed and designated as cP-1 and cP-2, respectively.     

Expression of hepatitis B virus middle and large surface antigen genes in Saccharomyces cerevisiae.

The hepatitis B virus genome carries the surface antigen (SAg) gene and an open reading frame that encodes two SAg-related polypeptides: SAg with a 55-amino-acid N-terminal extension polypeptide and SAg with a 174-amino-acid N-terminal extension polypeptide. These are termed middle S and large S, respectively. These polypeptides or their glycosylated derivatives have been detected in Dane particles, but their chemical and biological properties have remained largely unknown because of their limited availability. We attempted to produce these proteins in Saccharomyces cerevisiae by placing the coding regions under the control of the promoter of the yeast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene. Yeast cells carrying middle S and large S coding sequences produced 33,000- and 42,000-dalton products, respectively, each of which reacted with anti-S antibody and bound to polymerized human serum albumin, in accordance with the known properties of pre-S proteins from particles in human sera (K. H. Heermann, U. Goldmann, W. Schwartz, T. Seyffarth, H. Baumgarten, and W. 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, and M. Mayumi, Gastroenterology 86:910-918, 1984). The middle S polypeptide is glycosylated and can be assembled into particles whose size and density are similar to those of SAg. However, this polypeptide was highly susceptible to proteolytic degradation into 29,000- and 26,000-dalton polypeptides, of which only the former retained the binding activity to polymerized albumin. The large S polypeptides are nonglycosylated, relatively stable, and do not seem to assemble into particles by themselves.     

The position of heterologous epitopes inserted in hepatitis B virus core particles determines their immunogenicity.

The nucleocapsid (HBcAg) of the hepatitis B virus (HBV) has been suggested as a carrier moiety for vaccine purposes. We investigated the influence of the position of the inserted epitope within hybrid HBcAg particles on antigenicity and immunogenicity. For this purpose, genes coding for neutralizing epitopes of the pre-S region of the HBV envelope proteins were inserted at the amino terminus, the amino terminus through a precore linker sequence, the truncated carboxy terminus, or an internal site of HBcAg by genetic engineering and were expressed in Escherichia coli. All purified hybrid HBc/pre-S polyproteins were particulate. Amino- and carboxy-terminal-modified hybrid HBc particles retained HBcAg antigenicity and immunogenicity. In contrast, insertion of a pre-S(1) sequence between HBcAg residues 75 and 83 abrogated recognition of HBcAg by 5 of 6 anti-HBc monoclonal antibodies and diminished recognition by human polyclonal anti-HBc. Predictably, HBcAg-specific immunogenicity was also reduced. With respect to the inserted epitopes, a pre-S(1) epitope linked to the amino terminus of HBcAg was not surface accessible and not immunogenic. A pre-S(1) epitope fused to the amino terminus through a precore linker sequence was surface accessible and highly immunogenic. A carboxy-terminal-fused pre-S(2) sequence was also surface accessible but weakly immunogenic. Insertion of a pre-S(1) epitope at the internal site resulted in the most efficient anti-pre-S(1) antibody response. Furthermore, immunization with hybrid HBc/pre-S particles exclusively primed T-helper cells specific for HBcAg and not the inserted epitope. These results indicate that the position of the inserted B-cell epitope within HBcAg is critical to its immunogenicity.     

Isolation and characterization of cDNA encoding mouse RNA polymerase II subunit RPB14

By means of the yeast two-hybrid system using the 40-kDa subunit of mouse RNA polymerase I, mRPA40, as the bait, we isolated a mouse cDNA which encoded a protein with significant homology in amino acid sequence to the 12.5-kDa subunit of Saccharomyces cerevisiae RNA polymerase II, B12.5 (RPB11). Specific antibody raised against the recombinant protein that was derived from the cDNA reacted with a 14-kDa polypeptide in highly purified mammalian RNA polymerase II and did not react with any subunit of RNA polymerase I or III. Moreover, the antibody co-immunoprecipitated the largest subunit of mouse RNA polymerase II. These results provide biochemical evidence that the cDNA isolated, named mRPB14, encodes a specific subunit of RNA polymerase II, and indicate that the subunit organization of the enzyme is conserved between yeast and mouse. A possible role of the α-motif [Dequard-Chablat, M., Riva, M., Carles, C. and Sentenac, A., J. Biol. Chem. 266 (1991) 15300–15307] in the protein-protein interaction between mRPA40 and mRPB14 is also discussed.     

Cytochrome c oxidase from bakers' yeast. III. Physical characterization of isolated subunits and chemical evidence for two different classes of polypeptides.

Earlier studies have shown that cytochrome c oxidase from bakers' yeast is an oligomeric enzyme which contains three polypeptides (I to III) synthesized on mitochondrial ribosomes and four polypeptides (IV to VII) synthesized on cytoplasmic ribosomes. These polypeptide subunits have now been isolated by a simple protocol which utilizes differences in polypeptide charge, solubility, and size. Their molecular weights determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, gel filtration in the presence of guanidine hydrochloride, and amino acid analysis were: I, 40,000; II, 33,000; III, 22,000; IV, 14,500; V, 12,700; VI, 12,700; and VII, 4,600. All seven polypeptide subunits exhibited acidic isoelectric points; cytoplasmically made subunits were more acidic than mitochondrially made ones. The amino acid composition of two mitochondrially made subunits and two cytoplasmically made subunits was determined. The two mitochondrial translation products, I and II, contained only 34.7% and 42.1% polar amino acids, respectively, whereas the two cytoplasmic translation products, IV and VI, contained 48.3% and 49.3%, respectively. This agreed with the observation that Subunits I and II are very insoluble, requiring detergents for solubility, whereas Subunits IV and VI are water-soluble in the absence of any added detergent. These results indicate that the cytochrome c oxidase subunits synthesized on mitochondrial and cytoplasmic ribosomes are fundamentally different in size, isoelectric properties, and hydrophobicity. They also suggest the possibility that at least some of the mitochondrially made subunits are buried in the lipid phase of the mitochondrial inner membrane.     

Arabidopsis thaliana RNA polymerase II subunits related to yeast and human RPB5

Arabidopsis thaliana contains at least four genes that are predicted to encode polypeptides related to the RPB5 subunit found in yeast and human RNA polymerase II. This subunit has been shown to be the largest subunit common to yeast RNA polymerases I, II, and III (RPABC27). More than one of these genes is expressed in Arabidopsis suspension culture cells, but only one of the encoded polypeptides is found in purified RNA polymerases II and III. This polypeptide has a predicted pI of 9.6, matches 14 of 16 amino acids in the amino terminus of cauliflower RPB5 that was microsequenced, and shows 42 and 53% amino acid sequence identity with the yeast and human RPB5 subunits, respectively.     

Differential formation of disulfide linkages in the core antigen of extracellular and intracellular hepatitis B virus core particles.

Our understanding of the assembly of hepatitis B virus is still very limited. We present evidence to demonstrate that the HBc antigen formed oligomers through disulfide linkages in the extracellular hepatitis B virus core (HBc) particles. However, the intracellular HBV core particles did not contain disulfide-linked HBc antigens. Furthermore, the extracellular particles which had disulfide bonds were more stable than intracellular particles at pH 7.5 and 10 and in 3 M NaCl and 4 M urea. These data suggest that the formation of disulfide bonds in the HBc antigen is important for the integrity of the viral core particles.     

Topological Considerations of the 9-kDa Polypeptide which Contains Centers A and B, Associated with the 14- and 19-kDa Polypeptides in the Photosystem I Complex of Spinach

The topography of subunits around the 9-kDa polypeptide in thephotosystem I (PS I) complex of spinach was studied by examiningthe results of alkaline and chaotropic ion treatments, trypticdigestion, and cross-linking of thylakoid membranes supplementedwith Western blotting techniques using antibodies raised againstthe 9-, 14- and 19-kDa polypeptides. The 14- and 19-kDa polypeptideshave been shown to correspond to subunits III and II [Münchet al. (1988) Curr. Genet. 14: 511–518.], respectively,by a comparison of their respective amino acid compositionsand amino-terminal sequences [Oh-oka et al. (1988a) J. Biochem.103: 962–968.]. It appears that these three polypeptidesare peripheral proteins situated in close to each other on thestromal side of thylakoid membranes. The 9-kDa polypeptide withcenters A and B is stable within a specific environment of themembranes, in which the polypeptide is embedded under the twoother subunits, the 14- and 19-kDa polypeptides. Thus, the 9-kDapolypeptide becomes unstable when dissociated from the PS Icomplex and exposed to the solvent environment. (Received March 15, 1989; Accepted June 15, 1989)     

Comparative immunogenicity of hepatitis B virus core and E antigens

The nucleocapsid (hepatitis B core Ag (HBcAg] of the hepatitis B virus is a particulate Ag composed of a single polypeptide (p21). Although a non-particulate form of HBcAg designated hepatitis B e Ag (HBeAg) shares significant amino acid identity, the immune responses to these Ag appear to be regulated independently. This report describes the use of recombinant HBcAg and HBeAg to examine and compare murine T cell and B cell recognition of these related Ag. The HBcAg preparation was stable at pH 7.2 and 9.6 and expressed HBc antigenicity. However, the antigenicity of the HBeAg preparation was pH dependent. At pH 9.6 the HBeAg preparation was non-particulate and expressed HBe antigenicity exclusively; however, at pH 7.2 it was particulate and expressed both HBc and HBe antigenicities. Although this "hybrid" particle most likely does not exist naturally, it is a unique research reagent to investigate the interrelationship between HBcAg and HBeAg. HBcAg was significantly more immunogenic in terms of in vivo antibody production as compared to either the non-particulate or particulate forms of HBeAg. Nevertheless, in most murine strains HBcAg and HBeAg were equivalently immunogenic and crossreactive at the level of T cell activation. The disparity between anti-HBc and anti-HBe antibody production is best explained by the observation that HBcAg can function as a T cell-independent Ag whereas HBeAg is T cell dependent even when present within the same particulate structure as HBcAg. Furthermore, HBcAg was shown to function efficiently as an immunologic carrier moiety for the DNP hapten in athymic as well as euthymic mice in contrast to conventional carrier proteins. These results have implications relevant to the human immune responses to HBcAg and HBeAg during infection, and to vaccine development.     

Use of monoclonal antibodies in the assay of hepatitis B core antigen and antibody

Hybridoma cells secreting antibody against hepatitis B core antigen (HBc Ag) were prepared. BALB/c mice were immunized with 0.2 ml of purified HBc Ag, and their spleen cells were fused with mouse myeloma (P3U1) cells by means of polyethylene glycol 1000. Activities of antibodies against HBc Ag (anti-HBc) were tested by the immune adherence hemagglutination (IAHA) and reverse passive hemagglutination inhibition (RPHI) techniques. Hybridoma cells found to contain antibodies accounted for 26.5% by IAHA and 52.1% by RPHI, respectively. Among 32 monoclonal anti-HBc antibodies, 18 were found to be positive by both IAHA and RPHI, and the remaining 14 positive by RPHI only. After cloning, they were injected intraperitoneally into ascitic mice. The highest anti-HBc activity with an IAHA titer of 1:4 X 10(6) and with an RPHI titer of 1:1 X 10(5) was detected in this ascitic fluid. Enzyme immunoassay (EIA) and RPHI with monoclonal antibody containing the highest anti-HBc activity were developed. All the sera in which anti-HBc was detected by IAHA and RPHI with polyclonal antibody were positive in EIA. RPHI titers obtained with monoclonal antibody were in good agreement with usual IAHA and RPHI titers obtained with polyclonal antibody. These results indicate that monoclonal antibody can be used in the HBc Ag and anti-HBc assay system.     

Identification of hepatitis B virus polypeptides encoded by the entire pre-s open reading frame.

The open reading frame (ORF) that encodes the 226-amino-acid coat protein (hepatitis B virus surface antigen [HBsAg]) of hepatitis B virus has the potential to encode a 400-amino-acid polypeptide. The entire ORF would direct the synthesis of a polypeptide whose C-terminal amino acids represent HBsAg with an additional 174 amino acids at the N terminus (pre-s). Recently, virus particles have been shown to contain a polypeptide that corresponds to HBsAg with an additional 55 amino acids at the N terminus encoded by the DNA sequence immediately upstream of the HBsAg gene. A novel ORF expression vector containing the TAC promoter, the first eight codons of the gene for beta-galactosidase, and the entire coding sequence for chloramphenicol acetyltransferase was used in bacteria to express determinants of the 174 amino acids predicted from the pre-s portion of the ORF. The resulting tribrid protein containing 108 amino acids encoded by pre-s was expressed as one of the major proteins of bacteria harboring the recombinant plasmid. Single-step purification of the tribrid fusion protein was achieved by fractionation on a chloramphenicol affinity resin. Polyclonal antiserum generated to the fusion protein was capable of detecting 42- and 46-kilodalton polypeptides from virus particles; both polypeptides were also shown to contain HBsAg determinants. The ability of the polyclonal antiserum to identify polypeptides with these characteristics from virus particles presents compelling evidence that the DNA sequence of the entire ORF is expressed as a contiguous polypeptide containing HBsAg. The presence of multiple promoters and primary translation products from this single ORF argues that the function and potential interaction of the encoded polypeptides play a crucial role in the life cycle of the virus. Furthermore, the procedure and vector described in this report can be applied to other systems to facilitate the generation of antibodies to defined determinants and should allow the characterization of the epitope specificity of existing antibodies.     

Unusually high-level expression of a foreign gene (hepatitis B virus core antigen) in Saccharomyces cerevisiae

As a model system for the study of factors affecting gene expression, hepatitis B virus core antigen (HBcAg) has been expressed in the yeast Saccharomyces cerevisiae. The singularly high levels of expression achieved are approx. 40% of the soluble yeast protein. The HBcAg polypeptides are present as 28-nm particles which are morphologically indistinguishable from HBcAg particles in human plasma and are highly immunogenic in mice. The plasmid construction employed to achieve these very high levels of expression utilizes the constitutively active yeast promoter from the GAP491 gene which is fused in a way that all non-translated sequences flanking the HBcAg coding region are yeast-derived. Hybrid constructions containing 3'-nontranslated viral DNA (yeast 5') or 5'-nontranslated viral DNA (yeast 3') as well as a construction with both 5'- and 3'-nontranslated viral DNA also have been made. A comparison of these constructions for levels of HBcAg expression indicates that the strongest contributor to the high levels of protein is the presence of 5'-flanking sequences which are yeast-derived; secondarily, a significant improvement can be achieved if the 3'-flanking sequences also are yeast-derived. The high abundance of HBcAg in the highest producer is explicable in part on the basis of the very high stability in yeast cells of HBcAg polypeptides. Analysis of the HBcAg coding sequence reveals a very low index of codon bias for S. cerevisiae, largely discounting codon usage as a contributor to the high level of protein obtained.     

Plasmid dimerization increases the production of hepatitis B core particles in E. coli

Due to their icosahedral structure with a high density of B- and T-cell epitopes, hepatitis B virus (HBV) core (HBc) particles are used as components of novel anti-HBV vaccines. Previous experiments demonstrated that C-terminally truncated HBV core (HBcΔ) proteins, which lack the polyarginine domain, were produced more efficiently in E. coli compared with full-length HBc. We have established a tryptophan operon promoter-directed high-level production system of 145 amino acid HBcΔ (HBc145); however, the level of HBc145 synthesis varied among individual subclones. Further investigation revealed that the subclones exhibiting higher HBc145 synthesis also demonstrated plasmid dimerization, leading to HBc145 yields that were 60 ～ 65% (mg/g) or 25 ～ 30% (mg/L) higher compared to clones containing a monomeric plasmid. These data were confirmed in at least three independent expression and purification events. Although plasmid dimerization is generally considered to inhibit plasmid stability in a growing cell population, it was found to have a positive effect on HBc145 synthesis and production in both Trp-deficient and Trp-rich media. This finding should be considered when planning large-scale production of HBc145.     

Antigenic determinants and functional domains in core antigen and e antigen from hepatitis B virus.

The precore/core gene of hepatitis B virus directs the synthesis of two polypeptides, the 21-kilodalton subunit (p21c) forming the viral nucleocapsid (serologically defined as core antigen [HBcAg]) and a secreted processed protein (p17e, serologically defined as HBe antigen [HBeAg]). Although most of their primary amino acid sequences are identical, HBcAg and HBeAg display different antigenic properties that are widely used in hepatitis B virus diagnosis. To locate and to characterize the corresponding determinants, segments of the core gene were expressed in Escherichia coli and probed with a panel of polyclonal or monoclonal antibodies in radioimmunoassays or enzyme-linked immunosorbent assays, Western blots, and competition assays. Three distinct major determinants were characterized. The single conformational determinant responsible for HBc antigenicity in the assembled core (HBc) and a linear HBe-related determinant (HBe1) were both mapped to an overlapping hydrophilic sequence around amino acid 80; a second HBe determinant (HBe2) was assigned to a location in the vicinity of amino acid 138 but found to require for its antigenicity the intramolecular participation of the extended sequence between amino acids 10 and 140. It is postulated that HBcAg and HBeAg share common basic three-dimensional structure exposing the common linear determinant HBe1 but that they differ in the presentation of two conformational determinants that are either introduced (HBc) or masked (HBe2) in the assembled core. The simultaneous presentation of HBe1 and HBc, two distinctly different antigenic determinants with overlapping amino acid sequences, is interpreted to indicate the presence of slightly differently folded, stable conformational states of p21c in the hepatitis B virus nucleocapsid.     

Tumor antigens of human ad5 in transformed cells and in cells infected with transformation-defective host-range mutants

We have studied the polypeptides associated with the expression of the transforming region of the Ad5 genome by immunoprecipitating antigens (using the double antibody and protein A-Sepharose techniques) from cells infected with wild-type (wt) Ad5 or transformation-defective host range (hr) mutants and from cells transformed by Ad5. Three different antisera were used: P antiserum specific for early viral products (Russell et al., 1967) and two different hamster tumor antisera. Immunoprecipitation of antigens from wt-infected KB cells followed by SDS-polyacrylamide gel electrophoresis of precipitated proteins revealed that a major polypeptide having a molecular weight of approximately 58,000 was detected with all three antisera and with both the double antibody and the protein A-Sepharose techniques, while P antiserum also precipitated polypeptides of molecular weights 72,000, 67,000 and 44,000, which probably represent the DNA binding protein and related polypeptides, respectively. With the double antibody technique, in addition to the proteins mentioned above, P antiserum and the hamster tumor antisera precipitated a 10,500 dalton polypeptide which was not detected when the protein A-Sepharose procedure was used. Using either the double antibody or the protein A-Sepharose technique, we found that hr mutants from complementation group II failed to induce the synthesis of the 58,000 dalton protein, whereas mutants from complementation group I produced normal or near normal amounts. Using the double antibody technique, we found that the 10,500 dalton protein was absent or made in reduced amounts by group I mutants. A 58,000 dalton protein was detected in a number of different Ad5-transformed cell lines, including the 293 human line, the 14b hamster line and several transformed rat cell lines. This observation and the fact that transformation negative group II mutants fail to induce the synthesis of a 58,000 dalton polypeptide suggest that this protein is one of the Ad5-specific products necessary for cell transformation.     

抗乙型肝炎病毒e抗原和核心抗原双特异性单克隆抗体的建立与应用

用基因工程技术在大肠杆菌中高效表达的乙型肝炎病毒核心抗原(内含高滴度的e抗原)免疫Balb/C小鼠,取免疫小鼠脾细胞与小鼠骨髓瘤细胞(Sp2/0)融合,获得两株分泌高滴度既抗-HBe又抗-HBc的双特异性杂交瘤细胞系。细胞培养上清液中抗体滴度为100～1000以上;免疫腹水中的抗体滴度为8万至10万以上,均属IgG2a亚类。细胞在实验室连续传代二年多,仍保持高效分泌抗体能力。此单克隆抗体与HBeAg或HBcAg的结合可被抗-HBc或抗-HBc阳性血清所抑制,竞争抑制率在85.9％～96.8％之间。用此单克隆抗体与HBe的β型单克隆抗体和抗HBc的α型单克隆抗体配对,可组装成检测HBeAg/抗-HBe和抗-HBc的诊断试剂,具有重要的应用价值。     

Antibodies to the photosystem I chlorophyll a + b antenna cross-react with polypeptides of CP29 and LHCII

A chlorophyll (a + b)--protein complex associated with photosystem I (PSI) was isolated from a larger PSI complex (CPIa) produced by electrophoresis of barley thylakoids solubilized with 300 mM octyl glucoside. It had an apparent Mr of 35,000-43,000 on 7.5% and 10% acrylamide gels respectively, and a chlorophyll a/b ratio of 2.5 +/- 1.5. Denaturation released four polypeptides migrating between 21-24 kDa. They were well separated from the polypeptides of the two photosystem II chlorophyll a + b antenna complexes: LHCII (25-27 kDa) and CP29 (28-29 kDa). In order to study the PSI antenna complex, antibodies were raised against highly purified CPIa. The antigen appeared to be pure when electrophoresed, blotted and reacted with its antiserum, i.e. anti-CPIa detected only the 64-66-kDa CPI apoprotein and the four 21-24 kDa antenna polypeptides. However, when blotted against the whole spectrum of thylakoid proteins, it cross-reacted with both LHCII and CP29 apoproteins. Removal of anti-CPI activity from the anti-CPIa did not affect these cross-reactions, showing that they were not due to antibodies directed against CPI. To show that the same antibody population was reacting with both the photosystem I and photosystem II antenna polypeptides, anti-CPIa was adsorbed onto highly purified CPIa on nitrocellulose. The bound antibody was eluted and used again in a Western blot against whole thylakoid proteins. This selected antibody population showed the same relative strength of reaction with photosystem I and photosystem II antenna polypeptides as the original antibody population had. Similar observations have been made with antibodies to the two photosystem II antenna complexes. We therefore conclude that there are antigenic determinants in common among the chlorophyll a + b binding polypeptides, and predict that there could be amino acid sequence similarities.