Conformational characteristics of the complete sequence of group A streptococcal M6 protein

M protein is considered a virulence determinant on the streptococcal cell wall by virtue of its ability to allow the organism to resist attack by human neutrophils. The complete DNA sequence of the M6 gene from streptococcal strain D471 has allowed, for the first time, the study of the structural characteristics of the amino acid sequence of an entire M protein molecule. Predictive secondary structural analysis revealed that the majority of this fibrillar molecule exhibits strong alpha-helical potential and that, except for the ends, nonpolar residues in the central region of the molecule exhibit the 7-residue periodicity typical for coiled-coil proteins. Differences in this heptad pattern of nonpolar residues allow this central rod region to be divided into three subdomains which correlate essentially with the repeat regions A, B, and C/D in the M6 protein sequence. Alignment of the N-terminal half of the M6 sequence with PepM5, the N-terminal half of the M5 protein, revealed that 42% of the amino acids were identical. The majority of the identities were "core" nonpolar residues of the heptad periodicity which are necessary for the maintenance of the coiled coil. Thus, conservation of structure in a sequence-variable region of these molecules may be biologically significant. Results suggest that serologically different M proteins may be built according to a basic scheme: an extended central coiled-coil rod domain (which may vary in size among strains) flanked by functional end domains.     

Structural and biophysical properties of the integrin-associated cytoskeletal protein talin

Talin is a large cytoskeletal protein (2541 amino acid residues) which plays a key role in integrin-mediated events that are crucial for cell adhesion, migration, proliferation and survival. This review summarises recent work on the structure of talin and on some of the structurally better defined interactions with other proteins. The N-terminal talin head (approx. 50 kDa) consists of an atypical FERM domain linked to a long flexible rod (approx. 220 kDa) made up of a series of amphipathic helical bundle domains. The F3 FERM subdomain in the head binds the cytoplasmic tail of integrins, but this interaction can be inhibited by an interaction of F3 with a helical bundle in the talin rod, the so-called “autoinhibited form” of the molecule. The talin rod contains a second integrin-binding site, at least two actin-binding sites and a large number of binding sites for vinculin, which is important in reinforcing the initial integrin–actin link mediated by talin. The vinculin binding sites are defined by hydrophobic residues buried within helical bundles, and these must unfold to allow vinculin binding. Recent experiments suggest that this unfolding may be mediated by mechanical force exerted on the talin molecule by actomyosin contraction.     

Purification and characterization of a DnaK-like and a GroEL-like protein from Porphyromonas gingivalis

Heat-shock proteins of Porphyromonas gingivalis were demonstrated and two of them were purified and further characterized. The amplified de novo synthesis of two different proteins, with apparent molecular weights of 75 kDa and 68 kDa, was observed by autofluorography when a P. gingivalis culture incubated in a 14C-labeled amino acid mixture was shifted from 37 degrees C to 44 degrees C. Both proteins possessed ATP-binding abilities and were purified to almost homogeneity employing affinity chromatography on ATP-agarose followed by preparative SDS-PAGE. Purified 75 kDa and 68 kDa proteins had isoelectric points of 4.4 and 4.6, respectively. They were shown to be immunoreactive with commercial anti-DnaK and anti-GroEL polyclonal antibodies, respectively. Immunoblotting analysis of whole cells using antiserum raised against each purified protein from P. gingivalis, confirmed elevated synthesis of both proteins during thermal shock. A GroEL protein reacted strongly with antiserum against the 68 kDa protein. However, a DnaK protein reacted weakly with antiserum to the 75 kDa protein. Analysis of the N-terminal amino acid sequence of the DnaK-like protein (75 kDa) showed a high degree of homology with those of the HSP70 family including both prokaryotic and eukaryotic cells. The N-terminal amino acid analysis of the GroEL-like protein (68 kDa) indicated that it was identical to those of cloned GroEL homologues from P. gingivalis.     

The expression of multiple forms of troponin T in chicken-fast-skeletal muscle may result from differential splicing of a single gene

Troponin T isolated from chicken fast skeletal muscle has been shown to be present in three different molecular forms, one in breast and two in leg muscle. The three forms differ in both size and charge. Troponin T from breast muscle has a molecular mass of 33.5 kDa and a pI of about 7. Of the two leg muscle forms the larger has a molecular mass of 30.5 kDa and a pI of about 8.5 and the smaller a molecular mass of 29.8 kDa and a pI of about 10. Considerably more heterogeneity has been found in the leg than in the breast muscle proteins although this is not reflected in their N-terminal sequences. The reason for this is not clear. Troponin T from breast or leg muscle can be phosphorylated with troponin T kinase at the single serine residue at the N-terminus. No difference in the rate or extent of phosphorylation could be found between proteins from breast or leg muscle. The three proteins have been shown to differ only in the amino acid sequence of their N-terminal tryptic peptides. These peptides are of different length, that from breast troponin T being 58 residues and those from leg troponin T being 36 and 42 residues, these differences account for the difference in molecular mass of the parent proteins. Despite this difference the sequence of the first 12 and last 14 residues is identical in all three N-terminal peptides. The remainder of the sequence of the smallest peptide is also repeated in the other two but they each contain an extra piece of unique sequence. On the basis of these sequences it is proposed that chicken troponin T is coded for by a single gene containing, at the 5' end, a number of small exons and that three different mRNA molecules may be produced by alternative pathways of RNA splicing. The possible significance of these N-terminal sequence variations is discussed.     

The single-copy gene psbS codes for a phylogenetically intriguing 22 kDa polypeptide of photosystem II.

Recombinant phages that encode the complete precursor polypeptide for the 22 kDa polypeptide associated with photosystem II have been serologically selected from two lambda gt11 expression libraries made from polyadenylated RNA of spinach seedlings. The cDNAs hybridize to a 1.3 kb RNA species. The precursor protein is comprised of 274 amino acid residues and carries an N-terminal transit peptide of probably 69 amino acid residues. The mature protein exhibits four predicted transmembrane segments and is shown to be an integral component of photosystem II originating in a single-copy gene. The unique characteristics of this protein are: (i) it is the result of a gene-internal duplication of an ancestor with two membrane spans, (ii) a striking resemblance to LHC I/II, CP24/CP29 apoproteins, and ELIPs, although it does not bind chlorophyll and is present in cyanobacteria, and, as these proteins, (iii) it integrates into the membrane with uncleaved routing signals that display remarkable resemblance to patterns found in bipartite transit peptides.     

Molecular characterization of iron binding proteins, transferrin and ferritin heavy chain subunit, from the bumblebee Bombus ignitus

Transferrin and ferritin are iron-binding proteins involved in transport and storage of iron as part of iron metabolism. Here, we describe the cDNA cloning and characterization of transferrin (Bi-Tf) and the ferritin heavy chain subunit (Bi-FerHCH), from the bumblebee Bombus ignitus. Bi-Tf cDNA spans 2340 bp and encodes a protein of 706 amino acids and Bi-FerHCH cDNA spans 1393 bp and encodes a protein of 217 amino acids. Comparative analysis revealed that Bi-Tf appears to have residues comprising iron-binding sites in the N-terminal lobe, and Bi-FerHCH contains a 5'UTR iron-responsive element and seven conserved amino acid residues associated with a ferroxidase center. The Bi-Tf and Bi-FerHCH cDNAs were expressed as 79 kDa and 27 kDa polypeptides, respectively, in baculovirus-infected insect Sf9 cells. Northern blot analysis revealed that Bi-Tf exhibits fat body-specific expression and Bi-FerHCH shows ubiquitous expression. The expression profiles of the Bi-Tf and Bi-FerHCH in the fat body of B. ignitus worker bees revealed that Bi-Tf and Bi-FerHCH are differentially induced in a time-dependent manner in a single insect by wounding, bacterial challenge, and iron overload.     

Molecular structure of isolated MvspI, a variable surface protein of the fish pathogen Mycoplasma mobile

Mycoplasma mobile is a parasitic bacterium that causes necrosis in the gills of freshwater fishes. This study examines the molecular structure of its variable surface protein, MvspI, whose open reading frame encodes 2,002 amino acids. MvspI was isolated from mycoplasma cells by a biochemical procedure to 92% homogeneity. Gel filtration and analytical ultracentrifugation suggested that this protein is a cylinder-shaped monomer with axes of 66 and 2.7 nm. Rotary shadowing transmission electron microscopy of MvspI showed that the molecule is composed of two rods 30 and 45 nm long; the latter rod occasionally features a bulge. Immuno-electron microscopy and epitope mapping showed that the bulge end of the molecular image corresponds to the C terminus of the amino acid sequence. Partial digestion by various proteases suggested that the N-terminal part, comprised of 697 amino acids, is flexible. Analysis of the predicted amino acid sequence showed that the molecule features a lipoprotein and 16 repeats of about 90 residues; 15 positions exist between residues 88 and 1479, and the other position is between residues 1725 and 1807. The amino acid sequence of MvspI was mapped onto a molecular image obtained by electron microscopy. The present study is the first to elucidate the molecular shape of a variable surface protein of mycoplasma.     

Purification and characterization of the flagellar hook–basal body complex of Bacillus subtilis

The flagellar hook–basal body (HBB) complex of the Gram-positive bacterium Bacillus subtilis was purified and analysed by electron microscopy, gel electrophoresis, and amino acid sequencing of the major component proteins. The purified HBB complex consisted of the inner (M and S) rings, a rod and a hook. There were no outer (P and L) rings that are found in Gram-negative bacteria. The hook was 15 nm in thickness and 70 nm in length, which is thinner and longer than the hook of Salmonella typhimurium . The hook protein had an apparent molecular mass of 29 kDa, and its N-terminal sequence was identical to that of B. subtilis FlgG, which was previously reported as a rod protein. The sequence of the reported FlgG protein of B. subtilis is more closely related to that of FlgE (the hook protein) rather than FlgG (the rod protein) of S. typhimurium , in spite of the difference of the apparent molecular masses between the two hook proteins (29 kDa versus 42 kDa). The hook–basal body contained six major proteins (with apparent molecular masses of 82, 59, 35, 32, 29 and 20 kDa) and two minor proteins (23 kDa and 13 kDa), which consistently appeared from preparation to preparation. The N-terminus of each of these proteins was sequenced. Comparison with protein databases revealed the following polypeptide–gene correspondences: 82 kDa, fliF ; 59 kDa, flgK ; 35 kDa, orfF ; 32 kDa, yqhF ; 23 kDa, orf3 of the flaA locus; 20 kDa, flgB and flgC ; 13 kDa, not determined. The band at 20 kDa was a mixture of FlgB and FlgC, as revealed by two-dimensional gel analysis. Characteristic features of B. subtilis HBB are discussed in comparison with those of S. typhimiurium .     

Molecular characterization and high expression during oocyte development of a shrimp ovarian cortical rod protein homologous to insect intestinal peritrophins

Penaeoid shrimp oocytes nearing the completion of oogenesis are enveloped in an acellular vitelline envelope and possess extracellular cortical rods (CRs) that extended into the cortical cytoplasm. These cortical specializations are precursors of the jelly layer (JL) of the egg. In searching for highly expressed mRNAs during oogenesis in the marine shrimp (Penaeus semisulcatus), two related cDNAs have been isolated that encode a mature protein of 250 amino acid residues. The deduced amino acid sequences revealed the presence of repeated cysteine-rich domains that are related to the chitin-binding domains of insect intestinal peritrophins. Similar cysteine-rich domains were reported in insect intestinal mucin, crustacean tachycitin, and invertebrate chitinases. The shrimp ovarian peritrophin (SOP) is glycosylated and can bind chitin when extracted from CRs. Its apparent molecular mass in SDS-PAGE is 29-35 kDa and 33-36 kDa, under nonreducing or reducing conditions, respectively. SOP is a major protein of CRs and the JL, and was immunodetected in ovaries; purified CRs; fertilized eggs that were surrounded by a JL matrix; and in the cloudy, whitish flocculent material appearing in sea water immediately after spawning. Immunolocalization in tissue sections determined that SOP was present in oocyte cytoplasm and in extraoocytic CRs. Shrimp expressed SOP mRNA in ovaries at all oocyte developmental stages, whereas expression in the hepatopancreas was restricted to vitellogenic stages. SOP mRNA was abundant in the shrimp ovary and was detected before the presence of the corresponding protein. This is the first demonstration that a protein with similar features to insect intestinal peritrophins is a component of CRs and is therefore a main precursor of the JL of spawned shrimp eggs.     

Purification and Characterization of a DnaK-like and a GroEL-like Protein from Porphyromonas gingivalis

Heat-shock proteins of Porphyromonas gingivalis were demonstrated and two of them were purified and further characterized. The amplified de novo synthesis of two different proteins, with apparent molecular weights of 75 kDa and 68 kDa, was observed by autofluorography when a P. gingivalis culture incubated in a ¹⁴C-labeled amino acid mixture was shifted from 37°C to 44°C. Both proteins possessed ATP-binding abilities and were purified to almost homogeneity employing affinity chromatography on ATP-agarose followed by preparative SDS-PAGE. Purified 75 kDa and 68 kDa proteins had isoelectric points of 4.4 and 4.6, respectively. They were shown to be immunoreactive with commercial anti-DnaK and anti-GroEL polyclonal antibodies, respectively. Immunoblotting analysis of whole cells using antiserum raised against each purified protein from P. gingivalis, confirmed elevated synthesis of both proteins during thermal shock. A GroEL protein reacted strongly with antiserum against the 68 kDa protein. However, a DnaK protein reacted weakly with antiserum to the 75 kDa protein. Analysis of the N-terminal amino acid sequence of the DnaK-like protein (75 kDa) showed a high degree of homology with those of the HSP70 family including both prokaryotic and eukaryotic cells. The N-terminal amino acid analysis of the GroEL-like protein (68 kDa) indicated that it was identical to those of cloned GroEL homologues from P. gingivalis.     

Isolation and analysis of two cellulase cDNAs from Orpinomyces joyonii

Two cellulase cDNAs, celB29 and celB2, were isolated from a cDNA library derived from mRNA extracted from the anaerobic fungus, Orpinomyces joyonii strain SG4. The nucleotide sequences of celB2 and celB29 and the primary structures of the proteins encoded by these cDNAs were determined. The larger celB29 cDNA was 1966bp long and encoded a 477 amino acid polypeptide with a molecular weight of 54kDa. Analysis of the 1451bp celB2 cDNA revealed an 1164bp open reading frame coding for a 44kDa protein consisting of 388 amino acids. Both deduced proteins had a high sequence similarity in central regions containing putative catalytic domains. Primary structure analysis revealed that CelB29 contained a Thr/Pro-rich sequence that separated the N-terminal catalytic domain from a C-terminal reiterated region of unknown function. Homology analysis showed that both enzymes belong to glycosyl hydrolase family 5 and were most closely related to endoglucanases from the anaerobic fungi Neocallimastic patriciarum, Neocallimastix frontalis and Orpinomyces sp. The classification of CelB29 and CelB2 as endoglucanases was supported by enzyme assays. The cloned enzymes had high activities towards barley beta-glucan, lichenan and carboxymethylcellulose (CMC), but not Avicel, laminarin, pachyman, xylan and pullulan. In addition, CelB29 and CelB2 showed activity against p-nitrophenyl-beta-D-cellobioside (pNP-G(2)) to p-nitrophenyl-beta-D-cellopentaoside (pNP-G(5)) but not p-nitrophenyl-beta-D-glucopyranoside (pNP-G(1)) with preferential activity against p-nitrophenyl-beta-D-cellotrioside (pNP-G(3)). Based on these results, we proposed that CelB29 and CelB2 are endoglucanases with broad substrate specificities for short- and long-chain beta-1,4-glucans.     

Pea dehydrins: identification,characterisation and expression

An antiserum raised against dehydrin from maize (Zea mays) recognised several polypeptides in extracts of pea (Pisum sativum) cotyledons. A cDNA expression library was prepared from mRNA of developing cotyledons, screened with the antiserum and positive clones were purified and characterised. The nucleotide sequence of one such clone, pPsB12, contained an open reading frame which would encode a polypeptide with regions of significant amino acid sequence similarity to dehydrins from other plant species.The deduced amino acid sequence of the pea dehydrin encoded by B12 is 197 amino acids in length, has a high glycine content (25.9%), lacks tryptophan and is highly hydrophilic. The polypeptide has an estimated molecular mass of 20.4 kDa and pI=6.4. An in vitro synthesised product from the clone comigrates with one of the in vivo proteins recognised by the antiserum.A comparison of the pea dehydrin sequence with sequences from other species revealed conserved amino acid regions: an N-terminal DEYGNP and a lysine-rich block (KIKEKLPG), both of which are present in two copies. Unexpectedly, pea dehydrin lacks a stretch of serine residues which is conserved in other dehydrins.B12 mRNA and dehydrin proteins accumulated in dehydration-stressed seedlings, associated with elevated levels of endogenous abscisic acid (ABA). Applied ABA induced expression of dehydrins in unstressed seedlings. Dehydrin expression was rapidly reversed when seedlings were removed from the stress or from treatment with ABA and placed in water.During pea cotyledon development, dehydrin mRNA and proteins accumulated in mid to late embryogenesis. Dehydrin proteins were some of the most actively synthesised at about the time of maximum fresh weight and represent about 2% of protein in mature cotyledons.     

65-kilodalton protein phosphorylated by interleukin 2 stimulation bears two putative actin-binding sites and two calcium-binding sites

We have previously characterized a 65-kilodalton protein (p65) as an interleukin 2 stimulated phosphoprotein in human T cells and showed that three endopeptide sequences of p65 are present in the sequence of l-plastin [Zu et al. (1990) Biochemistry 29, 1055-1062]. In this paper, we present the complete primary structure of p65 based on the cDNA isolated from a human T lymphocyte (KUT-2) cDNA library. Analysis of p65 sequences and the amino acid composition of cleaved p65 N-terminal peptide indicated that the deduced p65 amino acid sequence exactly coincides with that of l-plastin over the C-terminal 580 residues [Lin et al. (1988) Mol. Cell. Biol. 8, 4659-4668] and has a 57-residue extension at the N-terminus to l-plastin. Computer-assisted structural analysis revealed that p65 is a multidomain molecule involving at least three intriguing functional domains: two putative calcium-binding sites along the N-terminal 80 amino acid residues; a putative calmodulin-binding site following the calcium-binding region; and two tandem repeats of putative actin-binding domains in its middle and C-terminal parts, each containing approximately 240 amino acid residues. These results suggest that p65 belongs to actin-binding proteins.     

Plateins: a novel family of signal peptide-containing articulins in euplotid ciliates

In euplotid ciliates, the cortex is reinforced by alveolar plates--proteinaceous scales located within the membranous alveolar sacs, forming a monolayer just below the plasma membrane. This system appears to play a cytoskeletal role analogous to that provided by the fibrous epiplasm found beneath the cortical alveoli in other ciliates. In Euplotes aediculatus, the major alveolar plate proteins (termed alpha-, beta-, and gamma-plateins) have been identified. Using anti-platein antibodies, an expression library of Euplotes genes was screened, and a platein gene identified, cloned, and completely sequenced. Comparison of its derived amino acid sequence with microsequences obtained directly from purified plateins identified this gene as encoding one of the closely related beta- or gamma-plateins. The derived protein, of 644 amino acids (74.9 kDa), is very acidic (pI = 4.88). Microsequences from authentic alpha-platein were then used to design oligonucleotide primers, which yielded, via a PCR-based approach, the sequences of two alpha-platein genes from E. aediculatus. Even more acidic proteins, the derived alpha1- and alpha2-plateins contain 536 and 501 residues, respectively. Analyses of their amino acid sequences revealed the plateins to be members of the articulin superfamily of cytoskeletal proteins, first described in Euglena and now identified in the ciliate Pseudomicrothorax and in Plasmodium. The hallmark articulin repetitive motifs (based on degenerate valine- and proline-rich 12-mers) are present in all three plateins. In beta/gamma-platein this primary motif domain (27 repeats) is central in the molecule, whereas the primary repeats in the alpha-plateins lie near their C-termini. A cluster of proline-rich pentameric secondary repeats is found in the C-terminus of beta/gamma-platein, but near the N-terminus of alpha-plateins. All three plateins contain canonical N-terminal signal sequences, unique among known cytoskeletal proteins. The presence of start-transfer sequences correlates well with the final intra-alveolar location of these proteins. This feature, and significant differences from known articulins in amino acid usage and arrangement within the repeat domains, lead us to propose that the plateins comprise a new family of articulin-related proteins. Efforts to follow microscopically the assembly of plateins into new alveolar plates during pre-fission morphogenesis are underway.     

Isolation and characterization of cDNA clones encoding the 17.9 and 8.1 kDa subunits of Photosystem I from Chlamydomonas reinhardtii

cDNA clones encoding two Photosystem I subunits of Chlamydomonas reinhardtii with apparent molecular masses of 18 and 11 kDa (thylakoid polypeptides 21 and 30; P21 and P30 respectively) were isolated using oligonucleotides, the sequences of which were deduced from the N-terminal amino acid sequences of the proteins. The cDNAs were sequenced and used to probe Southern and Northern blots. The Southern blot analysis indicates that both proteins are encoded by single-copy genes. The mRNA sizes of the two components are 1400 and 740 nucleotides, respectively. Comparison between the open reading frames of the cDNAs and the N-terminal amino acid sequences of the proteins indicates that the molecular masses of the mature proteins are 17.9 (P21) and 8.1 kDa (P30). Analysis of the deduced protein sequences predicts that both subunits are extrinsic membrane proteins with net positive charges. The amino acid sequences of the transit peptides suggest that P21 and P30 are routed towards the lumenal and stromal sides of the thylakoid membranes, respectively.Abbreviations OEE1, 2 and 3 oxygen evolution enhancer proteins 1, 2 and 3 - Rubisco ribulose bisphosphate carboxylase/oxygenase - PS photosystem - P21 and P30 C. reinhardtii thylakoid polypeptides 21 and 30     

Comparison of molecularly cloned bullous pemphigoid antigen to desmoplakin I confirms that they define a new family of cell adhesion junction plaque proteins.

Bullous pemphigoid is a subepidermal blistering disease in which patients have autoantibodies against the plaque of the hemidesmosome. Starting with a previously isolated 2-kilobase (kb) cDNA for bullous pemphigoid antigen (BPA), we used primer extension of keratinocyte mRNA to isolate overlapping cDNAs with a combined open reading frame of 6.3 kb, encoding most (243 kDa) of the BPA, but lacking the far amino terminus. Analysis of this amino acid sequence revealed a carboxyl-terminal domain containing two regions of 174 and 176 residues with high sequence identity. Most of the amino-terminal two-thirds of BPA is predicted to be in an alpha-helical conformation in which two chains would aggregate into a coiled-coil rod structure. BPA and desmoplakin I, a desmosome plaque protein, show remarkable sequence and structural homology. In its carboxyl-terminal domain, desmoplakin I also has 176 residue repeats with 40% sequence identity to those in BPA. The repeats in both molecules have a regular linear distribution of acidic and basic residues with a period of 9.5, the same as that found in the 1B segment of keratin filaments, suggesting a means of ionic interaction between keratin and these plaque proteins. Also, desmoplakin I, like BPA, is predicted to have a rod domain, which in both proteins has similar regular charge periodicities, suggesting a means of ionic self-aggregation. These findings extend those of Green et al. (Green, K. J., Parry, D. A. D., Steinert, P. S., Virata, L. A., Wagner, R. M., Angst, B. D., and Nilles, L. A. (1990) J. Biol. Chem. 265, 2603-2612) which show that BPA and desmoplakin I represent the first members of a new family of adhesion junction plaque proteins.     

beta-Granins: 21 kDa co-secreted peptides of the insulin granule closely related to adrenal medullary chromogranin A

Three closely related forms of a 21 kDa protein which is co-secreted with insulin have been purified and analysed. These differed in behaviour on ion-exchange chromatography but were indistinguishable by their susceptibility to staphylococcal V8 proteinase digestion, amino acid composition or N-terminal amino acid sequence. Their amino acid composition and N-terminal sequences were remarkably similar to adrenal medullary chromogranin A, a much larger protein (72 kDa). Antibodies to chromogranin A also reacted strongly with the 21 kDa protein in isolated insulin granules. It is concluded that the 21 kDa proteins either represent a repeated domain within the chromogranin molecule or a closely related gene product. The name beta-granin is proposed for these proteins.     

Isolation and characterization of complementary DNAs encoding human pregnancy-specific beta 1-glycoprotein

Pregnancy-specific beta 1-glycoprotein (PS beta G) isolated from human placenta consists of a set of at least three glycoproteins with apparent molecular masses of 72, 64, and 54 kDa, respectively. This heterogeneity is confirmed by the detection of three nonglycosylated polypeptides of 50, 48, and 36 kDa, which can be immunoprecipitated by antiserum to placental PS beta G obtained by in vitro translation of placental poly(A)+ RNA. To examine the structural relationships between these proteins, two cDNA clones of 1912 base pairs (PSG16) and 2131 base pairs (PSG93) encoding human PS beta Gs were isolated from a human placental lambda gt11 cDNA library. The sequenced portions of these two cDNAs are identical with the exception that clone PSG93 contains an additional 86 base pairs at the end of the common 3'-coding region. This insertion could result in the generation of a PS beta G species of 419 amino acid residues instead of the 417 amino acid residues predicted by the sequence of clone PSG16. The calculated molecular masses of the two polypeptides encoded by PSG16 and PSG93 are 46.9 and 47.2 kDa, close to the size of the major nonglycosylated PS beta G of 48 kDa. The identity of proteins coded for by these cDNA clones was confirmed by comparing the predicted amino acid sequences to sequences determined from endoproteinase Lys-C peptides obtained from human placental PS beta G. Two placental PS beta G mRNAs of 2200 bases (major) and 1700 bases (minor) have been detected by Northern hybridization analysis. Primer extension and S1 nuclease mapping experiments demonstrated that PS beta G mRNAs have heterogeneous 5' termini.