cDNA cloning and sequencing of component C9 of proteasomes from rat hepatoma cells

The nucleotide sequence of component C9 of rat proteasomes (multicatalytic proteinase complexes) has been determined from a recombinant cDNA clone isolated by screening a Reuber H4TG hepatoma cell cDNA library using synthetic oligodeoxynucleotide probes corresponding to partial amino acid sequences of the protein. The predicted sequence of C9 consists of 261 amino acid residues with a calculated molecular weight of 29,496. The C9 component is a novel protein, differing from known proteins, but its primary structure resembles those of other proteasome components, including C2, C3 and C5, although its similarity to C5 is relatively low, suggesting that proteasomes consist of a family of proteins that have evolved from a common ancestor.     

Molecular cloning of cDNA for proteasomes from rat liver: primary structure of component C3 with a possible tyrosine phosphorylation site

Proteasomes are multicatalytic proteinase complexes consisting of multiple components. Previously, we reported the cloning and sequencing of cDNA for the largest component, C2, of rat liver proteasomes [Fujiwara, T., Tanaka, K., Kumatori, A., Shin, S., Yoshimura, T., Ichihara, A., Tokunaga, F., Aruga, R., Iwanaga, S., Kakizuka, A., & Nakanishi, S. (1989) Biochemistry 28, 7332-7340]. In the present study, the nucleotide sequence of another component (C3) of proteasomes has been determined from a recombinant cDNA clone isolated by screening a rat liver cDNA library with synthetic oligodeoxynucleotide probes corresponding to partial amino acid sequences of the protein. The deduced sequence of component C3 consists of 234 amino acid residues with a calculated molecular weight of 25,925. These values are consistent with those obtained by protein chemical analyses. A single mRNA species hybridizing to the C3 cDNA of rat liver was expressed in all rat tissues examined and in a variety of other eukaryotic organisms, its distribution being similar to that of C2 mRNA. The wide distribution of the gene product, possibly C3, suggests that this protein functions similarly in most eukaryotes. C3 is an unmodified protein of a single gene and differs from any other known protein, but its overall amino acid sequence resembles those of other proteasomal components, including C2, suggesting that these components belong to a single family of proteins with the same evolutionary origin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular cloning of cDNA for proteasomes (multicatalytic proteinase complexes) from rat liver: primary structure of the largest component (C2)

Proteasomes (multicatalytic proteinase complexes) from rat liver are composed of at least 13 nonidentical components [Tanaka, K., Yoshimura, T., Ichihara, A., Ikai, A., Nishigai, M., Morimoto, M., Sato, M., Tanaka, N., Katsube, Y., Kameyama, K., & Takagi, T. (1988) J. Mol. Biol. 203, 985-996]. The nucleotide sequence of one major component (C2) of the proteasomes has been determined from a recombinant cDNA clone isolated by screening a rat liver cDNA library with a mixture of synthetic deoxyribonucleotides as a probe. The sequence was composed of 1174 nucleotides including a coding region for the entire protein and noncoding regions of both the 5'- and 3'-sides. The polypeptide deduced from the open reading frame consisted of 263 amino acid residues, and its molecular weight was calculated to be 29,516. The partial amino acid sequences of several fragments (approximately 45% of the total residues), which were obtained by cleavage of C2 with lysyl endopeptidase and cyanogen bromide, were determined by automated Edman degradation and found to be in complete accordance with those deduced from the cDNA sequence. The amino acid composition of C2, determined by chemical analysis, was also consistent with that deduced from the cDNA sequence, indicating that the cloned cDNA actually encoded component C2. Computer analysis revealed little structural similarity of C2 to other proteins reported so far. Northern blot hybridization analyses showed that the mRNA encoding this novel protein C2 was expressed in all the rat tissues examined and in a variety of eukaryotic organisms such as amphibia, birds, and mammals with slight species-specific differences in size.(ABSTRACT TRUNCATED AT 250 WORDS)     

PRS3 encoding an essential subunit of yeast proteasomes homologous to mammalian proteasome subunit C5.

We found by computer analysis that a putative yeast proteasome subunit gene named PRS3 that encodes a protein very similar to subunit C5 of rat and human proteasomes is located immediately 3' to the ERD2 gene of Saccharomyces cerevisiae. The similarity of the primary structures of the two suggests that this subunit may have a common function in proteasomes of all eukaryotes. The protein, deduced from the open reading frame of PRS3, consists of 242 amino acid residues with a calculated molecular weight of 27,077. Chromosomal disruption of the PRS3 gene created a recessive lethal mutation. Physical mapping by hybridization to intact S. cerevisiae chromosomal DNA showed that the PRS3 gene is located on chromosome II, unlike two other subunit genes, PRS1 and PRS2, which are located on chromosomes XV and VII, respectively. These findings indicate that the PRS3 protein is a subunit of yeast proteasomes that is essential for cell viability.     

Isolation and sequence of cDNA clones encoding rat phosphatidylinositol transfer protein

Phosphatidylinositol (PtdIns) transfer protein is a cytosolic protein that catalyzes the transfer of PtdIns between membranes. It is expressed in organisms from yeast to man, and activity has been found in all animal tissues examined. Using antibodies prepared against bovine brain PtdIns transfer protein, lambda gt11 rat brain cDNA libraries were screened and several clones isolated. DNA sequence analysis showed that the cDNAs encoded a polypeptide of 271 amino acids with a mass of 31,911 Da. Comparison of the deduced amino acid sequence with N-terminal sequence data obtained for the intact purified bovine brain protein and rat lung phospholipid transfer protein verified that the cDNAs were PtdIns transfer protein clones. The predicted protein shows no significant sequence similarity to other known (phospholipid)-binding proteins. DNA blot hybridization suggests that the rat genome may contain more than one gene encoding PtdIns transfer protein. RNA blot hybridization reveals that the PtdIns transfer protein gene is expressed at low levels in a wide variety of rat tissues; all tissues examined showed a major mRNA component of 1.9 kilobases and a minor component of 3.4 kilobases. The isolation of clones encoding rat PtdIns transfer protein will greatly facilitate studies of the structure and function of PtdIns transfer proteins and their role in lipid metabolism.     

Primary structure of Saccharomyces cerevisiae NADPH-cytochrome P450 reductase deduced from nucleotide sequence of its cloned gene

We isolated cDNA (pgCYR, about 2.1 kb) and genomic DNA (pgGYR, about 4 kb) clones coding for NADPH-cytochrome P450 reductase by immunoscreening of yeast Saccharomyces cerevisiae cDNA and genomic DNA libraries in phage lambda gt11. The clones were sequenced and found to encode a protein of 691 amino acid residues with a calculated molecular weight of 76,737 daltons. The amino-terminal sequence (excluding the initial methionine residue) deduced therefrom was in agreement with the protein sequence of the yeast reductase. In addition, the deduced sequence included the partial amino acid sequence determined with the papain-solubilized reductase. The total amino acid sequence of the yeast reductase showed 33-34% similarity with those of the rat, rabbit, pig, and trout reductases. In spite of low similarity in the total amino acid sequences, the possible functional domains related to binding of FAD, FMN, and NADPH were well conserved among all five species compared.     

Proteasomes (multi-protease complexes) as 20 S ring-shaped particles in a variety of eukaryotic cells

Latent multicatalytic protease complexes, named proteasomes, were purified to apparent homogeneity from various eukaryotic sources, such as human, rat, and chicken liver, Xenopus laevis ovary, and yeast (Saccharomyces cerevisiae), and their functional and structural properties were compared. They showed latency in breakdown of [methyl-3H]casein, but were greatly activated in various ways, such as by addition of polylysine. They all degraded three types of fluorogenic oligopeptides at the carboxyl side of basic, neutral, and acidic amino acids, and the three cleavage reactions showed different spectra for inhibition, suggesting that they had three distinct active sites. The proteasomes all seemed to be seryl endopeptidases with similar pH optima in the weakly alkaline region. Their physiochemical properties, such as their sedimentation coefficients (19 S to 22 S), diffusion coefficients (2.0-2.6 X 10(-7) cm2 s-1), molecular masses (700-900 kDa), and circular dichroic spectra, were similar. Their amino acid compositions were also very similar. Electron microscopy showed that they had similar well-defined symmetrical morphology, appearing to be ring-shaped particles with a small hole in the center. All the proteasomes seemed to be multisubunit complexes consisting of 15-20 polypeptides with molecular masses of 22-33 kDa and isoelectric points of pH 3-10, but they showed species-specific differences in subunit multiplicity. Moreover, they differed immunologically, as shown by Ouchterlony tests and immunoblotting analyses, although cross-immunoreactivities of some subunits or domains were observed. These results indicate that the sizes and shapes of these proteasomes have been highly conserved during evolution, but that they show species-specific differences in immunoreactivities and subunit structures. Thus proteasomes with similar structure and function seem to be ubiquitously distributed in eukaryotic organisms ranging from man to yeast. This distribution implies the general importance of these proteasomes for proteolysis.     

Nob1p, a new essential protein, associates with the 26S proteasome of growing saccharomyces cerevisiae cells

Nob1p, which interacts with Nin1p/Rpn12, a subunit of the 19S regulatory particle (RP) of the yeast 26S proteasome, has been identified by two-hybrid screening. NOB1 was found to be an essential gene, encoding a protein of 459 amino acid residues. Nob1p was detected in growing cells but not in cells in the stationary phase. During the transition to the stationary phase, Nob1p was degraded, at least in part, by the 26S proteasome. Nob1p was found only in proteasomal fractions in a glycerol gradient centrifugation profile and immuno-coprecipitated with Rpt1, which is an ATPase component of the yeast proteasomes. These results suggest that association of Nob1p with the proteasomes is essential for the function of the proteasomes in growing cells.     

Molecular analysis of complement component C8β and C9 cDNAs of Japanese flounder, Paralichthys olivaceus

 The amino acid sequences of the human terminal complement components show extensive structural similarity to each other. In this study the C8β and C9 cDNAs of Japanese flounder, Paralichthys olivaceus, were cloned and analyzed. The derived deduced amino acid sequences of the two terminal components were homologous to those of humans, in that the sequences of both species contained LDL receptor, EGF precursor, and two thrombospondin domains. Japanese flounder C9 was found to have a second thrombospondin region in the C-terminus, similar to that reported for rainbow trout and pufferfish. Moreover, these two complement component cDNAs of Japanese flounder had partial similarity to human perforin. These findings show that Japanese flounder C8β and C9 have similar structures, which supports the hypothesis that the terminal complement genes originated from the same ancestral gene. Collectively, these features emphasize the strong similarity among the members of the terminal complement family. Received: 23 March 1999 / Revised: 1 June 1999     

Phenylacetic acid stimulation of cellulose digestion by Ruminococcus albus 8.

The rate of cellulose digestion by Ruminococcus albus 8 grown on a defined medium could be increased by adding a minimum of 6.6% (vol/vol) rumen fluid. Strain 8 was grown on half this concentration, and the culture medium before and after growth was analyzed by gas chromatography-mass spectrometry to determine which components of the rumen fluid were used. Phenylacetic acid was identified as the component needed to make the defined medium nutritionally equivalent to one supplemented with rumen fluid. [14C]phenylacetic acid fed to cultures of strain 8 was primarily incorporated into protein. Hydrolysis of protein samples and separation of the resulting amino acids showed that only phenylalanine was labeled. The results indicate that cellulose digestion by strain 8 was probably limited by phenylalanine biosynthesis in our previously reported medium. The data obtained on the utilization of other rumen fluid components, as well as on the production of metabolites, illustrate the potential usefulness of this method in formulating defined media to simulate those in nature.     

Biosynthesis of riboflavin: an unusual riboflavin synthase of Methanobacterium thermoautotrophicum.

Riboflavin synthase was purified by a factor of about 1,500 from cell extract of Methanobacterium thermoautotrophicum. The enzyme had a specific activity of about 2,700 nmol mg(-1) h(-1) at 65 degrees C, which is relatively low compared to those of riboflavin synthases of eubacteria and yeast. Amino acid sequences obtained after proteolytic cleavage had no similarity with known riboflavin synthases. The gene coding for riboflavin synthase (designated ribC) was subsequently cloned by marker rescue with a ribC mutant of Escherichia coli. The ribC gene of M. thermoautotrophicum specifies a protein of 153 amino acid residues. The predicted amino acid sequence agrees with the information gleaned from Edman degradation of the isolated protein and shows 67% identity with the sequence predicted for the unannotated reading frame MJ1184 of Methanococcus jannaschii. The ribC gene is adjacent to a cluster of four genes with similarity to the genes cbiMNQO of Salmonella typhimurium, which form part of the cob operon (this operon contains most of the genes involved in the biosynthesis of vitamin B12). The amino acid sequence predicted by the ribC gene of M. thermoautotrophicum shows no similarity whatsoever to the sequences of riboflavin synthases of eubacteria and yeast. Most notably, the M. thermoautotrophicum protein does not show the internal sequence homology characteristic of eubacterial and yeast riboflavin synthases. The protein of M. thermoautotrophicum can be expressed efficiently in a recombinant E. coli strain. The specific activity of the purified, recombinant protein is 1,900 nmol mg(-1) h(-1) at 65 degrees C. In contrast to riboflavin synthases from eubacteria and fungi, the methanobacterial enzyme has an absolute requirement for magnesium ions. The 5' phosphate of 6,7-dimethyl-8-ribityllumazine does not act as a substrate. The findings suggest that riboflavin synthase has evolved independently in eubacteria and methanobacteria.     

Isolation of a cDNA encoding the rat liver S-adenosylmethionine synthetase

We have isolated cDNA clones encoding the rat liver S-adenosylmethionine synthetase by means of immunological screening from a phage lambda gt 11 expression library containing cDNA synthesized from adult rat liver poly(A)-RNA. The amino acid sequence deduced from the cDNA indicates that the rat liver enzyme for this protein contains 397 amino acid residues and has a molecular mass of 43697 Da. The deduced amino acid sequence of rat liver S-adenosylmethionine synthetase was 68% similar to those of yeast S-adenosylmethionine synthetases encoded by two unlinked genes SAM1 and SAM2. The rat liver S-adenosylmethionine synthetase also shows 52% similarity with the deduced amino acid sequence of the MetK gene encoding the S-adenosylmethionine synthetase in Escherichia coli.     

The mammalian homolog of yeast Sec13p is enriched in the intermediate compartment and is essential for protein transport from the endoplasmic reticulum to the Golgi apparatus.

The role of COPII components in endoplasmic reticulum (ER)-Golgi transport, first identified in the yeast Saccharomyces cerevisiae, has yet to be fully characterized in higher eukaryotes. A human cDNA whose predicted amino acid sequence showed 70% similarity to the yeast Sec13p has previously been cloned. Antibodies raised against the human SEC13 protein (mSEC13) recognized a cellular protein of 35 kDa in both the soluble and membrane fractions. Like the yeast Sec13p, mSEC13 exist in the cytosol in both monomeric and higher-molecular-weight forms. Immunofluorescence microscopy localized mSEC13 to the characteristic spotty ER-Golgi intermediate compartment (ERGIC) in cells of all species examined, where it colocalized well with the KDEL receptor, an ERGIC marker, at 15 degrees C. Immunoelectron microscopy also localized mSEC13 to membrane structures close to the Golgi apparatus. mSEC13 is essential for ER-to-Golgi transport, since both the His6-tagged mSEC13 recombinant protein and the affinity-purified mSEC13 antibody inhibited the transport of restrictive temperature-arrested vesicular stomatitis virus G protein from the ER to the Golgi apparatus in a semi-intact cell assay. Moreover, cytosol immunodepleted of mSEC13 could no longer support ER-Golgi transport. Transport could be restored in a dose-dependent manner by a cytosol fraction enriched in the high-molecular-weight mSEC13 complex but not by a fraction enriched in either monomeric mSEC13 or recombinant mSEC13. As a putative component of the mammalian COPII complex, mSEC13 showed partially overlapping but mostly different properties in terms of localization, membrane recruitment, and dynamics compared to that of beta-COP, a component of the COPI complex.     

Nuclear proteasomes carry a constitutive posttranslational modification which derails SDS-PAGE (but not CTAB-PAGE)

We report that subunits of human nuclear proteasomes carry a previously unrecognised, constitutive posttranslational modification. Subunits with this modification are not visualised by SDS-PAGE, which is used in almost all denaturing protein gel electrophoresis. In contrast, CTAB-PAGE readily visualises such modified subunits. Thus, under most experimental conditions, with identical samples, SDS-PAGE yielded gel electrophoresis patterns for subunits of nuclear proteasomes which were misleading and strikingly different from those obtained with CTAB-PAGE. Initial analysis indicates a novel modification of a high negative charge with some similarity to polyADP-ribose, possibly explaining compatibility with (positively-charged) CTAB-PAGE but not (negatively-charged) SDS-PAGE and providing a mechanism for how nuclear proteasomes may interact with chromatin, DNA and other nuclear components.     

Molecular cloning of an Arabidopsis cDNA encoding a dynamin-like protein that is localized to plastids

Dynamin-related proteins are high molecular weight GTPase proteins found in a variety of eukaryotic cells from yeast to human. They are involved in diverse biological processes that include endocytosis in animal cells and vacuolar protein sorting in yeast. We isolated a new gene, ADL2, that encodes a dynamin-like protein in Arabidopsis. The ADL2 cDNA is 2.68 kb in size and has an open reading frame for 809 amino acid residues with a calculated molecular mass of 90 kDa. Sequence analysis of ADL2 revealed a high degree of amino acid sequence similarity to other members of the dynamin superfamily. Among those members ADL2 was most closely related to Dnm1p of yeast and thus appears to be a member of the Vps1p subfamily. Expression studies showed that the ADL2 gene is widely expressed in various tissues with highest expression in flower tissues. In vivo targeting experiments showed that ADL2:smGFP fusion protein is localized to chloroplasts in soybean photoautroph cells. In addition experiments with deletion constructs revealed that the N-terminal 35 amino acid residues were sufficient to direct the smGFP into chloroplasts in tobacco protoplasts when expressed as a fusion protein.     

Proteasomes are essential for yeast proliferation. cDNA cloning and gene disruption of two major subunits.

The cDNAs encoding two major subunits, named YC1 and YC7-alpha, of yeast proteasomes (multicatalytic proteinase complexes) were isolated and sequenced. As deduced from their nucleotide sequences, YC1 and YC7-alpha consist of 288 and 252 amino acid residues with calculated molecular weights of 31,534 and 27,999, respectively. They showed marked sequence homology to other eukaryotic proteasome components, suggesting that proteasomes are composed of a family of subunits with the same evolutional origin. To obtain information on the physiological role of proteasomes, we disrupted the chromosomal genes of YC1 and YC7-alpha of yeast cells independently, using isolated cDNA clones. Disruption of the coding region of one copy of the YC1 gene in diploid yeast created a recessive lethal mutation, but disruption of the 3'-noncoding region of the gene had no effect on cell proliferation. Disruption of the YC7-alpha gene also had a lethal effect on haploid yeast cells. These findings demonstrated that YC1 and YC7-alpha are both encoded by a single copy gene and that these genes are essential for proliferation of yeast cells.     

Molecular cloning and functional analysis of three subunits of yeast proteasome.

The genes encoding three subunits of Saccharomyces cerevisiae proteasome were cloned and sequenced. The deduced amino acid sequences were homologous not only to each other (30 to 40% identity) but also to those of rat and Drosophila proteasomes (25 to 65% identity). However, none of these sequences showed any similarity to any other known sequences, including various proteases, suggesting that these proteasome subunits may constitute a unique gene family. Gene disruption analyses revealed that two of the three subunits (subunits Y7 and Y8) are essential for growth, indicating that the proteasome and its individual subunits play an indispensable role in fundamental biological processes. On the other hand, subunit Y13 is not essential; haploid cells with a disrupted Y13 gene can proliferate, although the doubling time is longer than that of cells with nondisrupted genes. In addition, biochemical analysis revealed that proteasome prepared from the Y13 disrupted cells contains tryptic and chymotryptic activities equivalent to those of nondisrupted cells, indicating that the Y13 subunit is not essential for tryptic or chymotryptic activity. However, the chymotryptic activity of the Y13 disrupted cells is not dependent on sodium dodecyl sulfate (SDS), an activator of proteasome, since nearly full activity was observed in the absence of SDS. Thus, the activity in proteasome of the Y13 disrupted cells might result in unregulated intracellular proteolysis, thus leading to the prolonged cell cycle. These results indicate that cloned proteasome subunits having similar sequences to the yeast Y13 subunit are structural, but not catalytic, components of proteasome. It is also suggested that two subunits (Y7 and Y8) might occupy positions essential to proteasome structure or activity, whereas subunit Y13 is in a nonessential but important position.     

Nucleotide sequence analysis of the 3'-terminal region of two Korean isolates of lily symptomless Carlavirus and expression of the coat protein in E. coli.

The 3'-terminal regions of the genomic RNAs of two Korean isolates of the lily symptomless Carlavirus (LSV), LSV-Ko and LSV-KII, were cloned and their nucleotide sequences were determined. The nucleotide sequence analysis and protein analysis by the Western blot revealed that E. coli expressed a 32-kDa protein that is the viral coat protein (CP) for the LSV. The two Korean strains share 98.4% and 98.3% sequence identities at the nucleotide and amino acid levels, respectively. The CP gene of LSV-Ko showed 99.1% and 87.0% nucleotide sequence identities, and 99.0% and 96.6% amino acid sequence identities with those of the Netherlands and the Japanese LSV strains, respectively. A pairwise amino acid sequence comparison revealed a sequence similarity of 29.6% to 69.8% between LSV-Ko and other species of the carlavirus. The 16 kDa protein of LSV-Ko shares 17.6% to 42.7% amino acid similarity with those of 8 other the carlaviruses, and they are variable in the N-terminal region. The Cys repeated zinc finger nucleic acid binding domain was found in the 16 kDa protein for all of the LSV strains. Sequence comparisons of the 7 kDa protein of LSV in the strain level showed significant identities from 100.0% to 98.4%. LSV-Ko shares 21.9% to 42.2% amino acid similarity with those of 8 other carlaviruses, 4 members of the potexviruses, and a closterovirus. LSV is closely related to blueberry scorch virus (BISV) based upon the phylogenetic tree analyses of the three proteins, indicating LSV to be a quite distinct member of the genus Carlavirus.     

The OLE1 gene of Saccharomyces cerevisiae encodes the delta 9 fatty acid desaturase and can be functionally replaced by the rat stearoyl-CoA desaturase gene

Strains of Saccharomyces cerevisiae bearing the ole1 mutation are defective in unsaturated fatty acid (UFA) synthesis and require UFAs for growth. A previously isolated yeast genomic fragment complementing the ole1 mutation has been sequenced and determined to encode the delta 9 fatty acid desaturase enzyme by comparison of primary amino acid sequence to the rat liver stearoyl-CoA desaturase. The OLE1 structural gene encodes a protein of 510 amino acids (251 hydrophobic) having an approximate molecular mass of 57.4 kDa. A 257-amino acid internal region of the yeast open reading frame aligns with and shows 36% identity and 60% similarity to the rat liver stearoyl-CoA desaturase protein. This comparison disclosed three short regions of high consecutive amino acid identity (greater than 70%) including one 11 of 12 perfect residue match. The predicted yeast enzyme contains at least four potential membrane-spanning regions and several shorter hydrophobic regions that align exactly with similar sequences in the rat liver protein. An ole1 gene-disrupted yeast strain was transformed with a yeast-rat chimeric gene consisting of the promoter region and N-terminal 27 codons of OLE1 fused to the rat desaturase coding sequence. Fusion gene transformants displayed near equivalent growth rates and modest lipid composition changes relative to wild type yeast control implying a significant conservation of delta 9 desaturase tertiary structure and efficient interaction between the rat desaturase and yeast cytochrome b5.     

The gene encoding a major component of the lateral elements of synaptonemal complexes of the rat is related to X-linked lymphocyte-regulated genes.

The lateral elements of synaptonemal complexes (SCs) of the rat contain major components with relative electrophoretic mobilities (M(r)S) of 30,000 and 33,000. After one-dimensional separation of SC proteins on polyacrylamide-sodium dodecyl sulfate gels, these components show up as two broad bands. These bands contain closely related proteins, as judged from their peptide maps and immunological reactivity. Using affinity-purified polyclonal anti-30,000- and anti-33,000-M(r) component antibodies, we isolated a cDNA encoding at least one of the 30,000- or 33,000-M(r) SC components. The protein predicted from the nucleotide sequence of the cDNA, called SCP3 (for synaptonemal complex protein 3), has a molecular mass of 29.7 kDa and a pI value of 9.4. It has a potential nucleotide binding site and contains stretches that are predicted to be capable of forming coiled-coil structures. In the male rat, the gene encoding SCP3 is transcribed exclusively in the testis. SCP3 has significant amino acid similarity to the pM1 protein, which is one of the predicted products of an X-linked lymphocyte-regulated gene family of the mouse: there are 63% amino acid sequence similarity and 35% amino acid identity between the SCP3 and pM1 proteins. However, SCP3 differs from pM1 in several respects, and whether the proteins fulfill related functions is still an open question.