Myrosinase: gene family evolution and herbivore defense in Brassicaceae

Glucosinolates are a category of secondary products present primarily in species of the order Capparales. When tissue is damaged, for example by herbivory, glucosinolates are degraded in a reaction catalyzed by thioglucosidases, denoted myrosinases, also present in these species. Thereby, toxic compounds such as nitriles, isothiocyanates, epithionitriles and thiocyanates are released. The glucosinolate-myrosinase system is generally believed to be part of the plant's defense against insects, and possibly also against pathogens. In this review, the evolution of the system and its impact on the interaction between plants and insects are discussed. Further, data suggesting additional functions in the defense against pathogens and in sulfur metabolism are reviewed.

Myrosinase: gene family evolution and herbivore defense in Brassicaceae

Glucosinolates are a category of secondary products present primarily in species of the order Capparales. When tissue is damaged, for example by herbivory, glucosinolates are degraded in a reaction catalyzed by thioglucosidases, denoted myrosinases, also present in these species. Thereby, toxic compounds such as nitriles, isothiocyanates, epithionitriles and thiocyanates are released. The glucosinolate-myrosinase system is generally believed to be part of the plant's defense against insects, and possibly also against pathogens. In this review, the evolution of the system and its impact on the interaction between plants and insects are discussed. Further, data suggesting additional functions in the defense against pathogens and in sulfur metabolism are reviewed.

Age-dependent wound induction of a myrosinase-associated protein from oilseed rape (Brassica napus)

In order to study the expression of the induced form of myrosinase-associated protein (iMyAP), a genomic clone encoding the protein was isolated from Brassica napus. The coding portion of the gene was found to consist of five exons separated by one long intron of 938 bp and three shorter introns of ca. 100 bp. A 1.9 kb promoter fragment including the 5'-untranslated region was cloned in front of the coding portion of the Escherichia coli iudA gene and transformed into Arabidopsis thaliana. Expression was observed in hypocotyls of 4-day seedlings, but in 7-day seedlings the iMyAP promoter did not direct expression. In flowering plants, only the abscission zone of the young silique displayed promoter activity. In contrast, mechanical wounding of 7-day seedlings induced a systemic expression in all cells of the cotyledons. Wounding of 14-day seedlings gave rise to systemic induced expression mainly in the vascular tissue. However, mechanical wounding and wounding by flea beetles (Phyllotreta undulata) of 4-week old plants only gave rise to a local induction of the promoter, suggesting that the systemic signal system is age-dependent. Methyl jasmonate also induced iMyAP expression. In situ and northern analysis of iMyAP transcripts in young leaves of B. napus showed that the induction was high after 1 h and absent after 24 h. Comparison of the effect of different types of wounding on the iMyAP promoter induction in transgenic Arabidopsis showed that similar degrees of local induction were achieved regardless of the degree of macerated tissue left on the plant.

Interaction between composite elements in the napA promoter: both the B-box ABA-responsive complex and the RY/G complex are necessary for seed-specific expression

During seed maturation, the transcriptional activity of napin genes is regulated by developmental signals involving the transcriptional activator ABI3 and abscisic acid (ABA). To localize cis elements involved in the seed-specific activity of the napin napA promoter, a systematic analysis was performed focusing on two major element complexes, the B-box and RY/G. Substitution mutation analysis using promoter-reporter gene fusions in stable transgenic tobacco showed synergistic interactions between elements within these complexes. The distal part of the B-box shows similarities to abscisic acid response elements and the proximal portion contains a CA-rich element. In vitro studies involving Exonuclease III protection and electrophoretic mobility shift assays revealed binding by nuclear proteins to elements within the B-box. The distal and proximal parts of the B-box were found to bind distinct nuclear protein complexes. By gain-of-function analysis with a tetramer of the B-box fused to a truncated (-46) cauliflower mosaic virus (CaMV) 35S minimal promoter, it was demonstrated that the B-box mediates strong activity in seeds. Further, it was shown that the elements in the B-box constitute an ABA-responsive complex, since the B-box tetramer mediates ABA-responsiveness in vegetative tissues to a construct containing the CaMV virus 35S enhancer (-343 to -90). Thus, the seed-specific activity of the napA promoter relies on the combinatorial interaction between the RY/G complex and the B-box ABA-responsive complex during the ABA response in seed development.

Effects of extracellular calcium on the subcellular translocation of bovine parathyroid PKC isozymes

The release of parathyroid hormone is regulated by the extracellular concentration of Ca2+ through a sensor(s) on the surface of the parathyroid cells, but few details are known on the further relay of the signal inside the cell. Activation of protein kinase C (PKC) isozymes is associated with their translocation from the cell soluble fraction to the particulate fraction of the cell. Therefore, identification of a subcellular localization of a PKC isozyme in parathyroid cells as a response to changes in extracellular Ca2+ should be an indication for its putative role in signal transduction coupled to the Ca2+ sensor. We have determined the subcellular localization of six PKC isozymes (alpha, betaI, betaII, epsilon, zeta, and iota) in nonstimulated parathyroid cells and in those treated with low (0.5 mM) and high (3.0 mM) extracellular Ca2+ by confocal microscopy. At the physiological concentration of serum Ca2+, all PKC isozymes studied were localized mainly to the cytosol, although to different extents. Low extracellular Ca2+ caused a redistribution of PKCalpha to the periphery of the cells. In contrast, PKCbetaI, -epsilon, -zeta, and -iota were translocated to the periphery of the cells at high extracellular Ca2+. These results indicate that PKCalpha, -betaI, -epsilon, -zeta, and -iota are involved in the response of parathyroid cells to changes in extracellular Ca2+.

The role of protein kinase C signaling in activated DRA transcription

Expression of human MHC HLA-DRA class II gene can be up-regulated in B cells by Ig cross-linking as well as by phorbol esters such as 12-O-tetradecanoyl phorbol 13-acetate (TPA). Induced DRA expression involves activation of restricted protein kinase C (PKC) isoforms, resulting in activated activator protein-1-dependent transcription. In this report expression profiles and activation of PKC were analyzed in human Raji B lymphoblastoid cells. Transient transfection analysis with target plasmids containing either DRA promoter (wild-type or mutated) or TPA response elements demonstrated that pretreatment with the selective PKC inhibitor GF 109203X repressed TPA-mediated activation. Western analysis performed on cellular fractions of resting cells and of TPA-activated cells revealed abundant expression of classical PKC-alpha (cPKC-alpha), cPKC-betaII, and atypical PKC-zeta isoforms and identified a sustained translocation of cPKC-alpha and cPKC-betaII from the cytosolic compartment to membranes. As expected, the distribution of atypical PKC-zeta was unaffected by TPA treatment and displayed an even distribution between cytosol and membranes. This finding was confirmed by immunofluorescence microscopy. The TPA-mediated translocation of cPKC-alpha and cPKC-betaII was not influenced by pretreatment with GF 109203X. Finally, functional activation and translocation of PKC were investigated with a selective in vitro kinase assay. Together, these results show that activated HLA-DRA expression in response to TPA treatment is strictly dependent on PKC activation acting on the X2 box of the DRA promoter and that selective inhibition of PKC enzymatic activity does not influence subcellular localization of expressed PKC isoenzymes. Thus, the translocation event per se occurs independently of PKC activation in these cells.

Molecular cloning and characterization of starch-branching enzyme II from potato

Full-length cDNA for starch branching enzyme (SBE) II of potato was isolated and sequenced. In potato, similarly to most other investigated plants, the SBE-II isoform differs from SBE-I by having an acidic amino-terminal extension and a shorter carboxyterminus. Two forms of SBE-II, migrating as 98 and 95 kDa proteins in 6% SDS-polyacrylamide gels, were associated to tuber starch. The latter form was 16 amino acids shorter in the amino terminus. Transcript of SBE-II was present in leaf tissue, whereas significant expression was not seen in tubers. On the other hand, a significant amount of SBE-I transcript was detected in tuber tissue but not in leaves.

Retroelements in the human MHC class II region

Molecular genetic studies of the human major histocompatibility complex (MHC) have led to the identification of more than 200 genes. Besides the large number of genes in the MHC, densely clustered areas of retroelements have been identified. These include short and long interspersed elements (SINEs and LINEs), and human endogenous retroviruses (HERVs). The presence of retroelements in the MHC provides a clear example of how these elements affect the genome plasticity of the host. Comparative analyses of these retroelements have proven highly useful in evolutionary studies of the MHC. Recently, HERV-encoded superantigens have been implicated as candidate autoimmune genes in type I diabetes and multiple sclerosis. In addition, genetic analyses have revealed that autoimmune diseases show strong associations with MHC class II genes. The intriguing correlations between retroviral encoded antigens, MHC class II genes and the development of autoimmune disease merit intense future investigations of retroelements, in particular those endogenous retroviruses located in the MHC class II region proper.

The myrosinase-binding protein from Brassica napus seeds possesses lectin activity and has a highly similar vegetatively expressed wound-inducible counterpart

This communication demonstrates that proteins in the family of myrosinase-binding proteins (MBP) present in seeds of Brassica napus possess lectin activity, binding most efficiently to p-aminophenyl alpha-D-mannopyranoside-agarose, and to some extent to N-acetylglucosamine-agarose. A cDNA encoding a vegetatively expressed, wound-inducible counterpart to these seed MBP was isolated and characterised. Upon wounding, this MBP transcript accumulated in old and young leaves, and was systemically expressed in the young plant. Additionally, the wound-induced MBP transcript increased in abundance after treating the young plants with methyl jasmonate (MeJA), jasmonic acid (JA) or abscisic acid (ABA), and to some extent in response to the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. Expression induced by wounding, ABA or JA was antagonised by simultaneous feeding of the plants with salicylic acid. MBP polypeptides accumulated in MeJA-treated plants. The myrosinases redistributed from the soluble fraction into the insoluble fraction of a tissue extract after induction. The most abundant MBP (94 kDa) partitioned in the insoluble fraction, while two larger MBP (103 kDa and 108 kDa) were present only in the soluble fraction of extracts obtained from the control or MeJA-treated plant tissues.

Molecular cloning and N-terminal analysis of bovine cystatin C. Identification of a full-length N-terminal region

The N-terminal region of human cystatin C has been shown to be of crucial importance for the interaction of the inhibitor with cysteine proteinases. However, several studies have been unable to identify the corresponding region in bovine cystatin C, indicating that the binding of proteinases to the bovine inhibitor may not be dependent on this region. With the aim to resolve this apparent discrepancy and to elucidate the relation of bovine cystatin C to other cystatins, we have isolated a cDNA clone encoding bovine precystatin C. The sequence of this cDNA was similar to that of the human inhibitor and showed a putative signal peptidase cleavage site consistent with the N-terminal regions of the bovine and human inhibitors being of comparable size. This suggestion was verified by determination of the relative molecular mass of the mature bovine inhibitor isolated from cerebrospinal fluid under conditions minimising proteolysis. The N-terminal of the purified inhibitor was blocked, but the sequence of the N-terminal peptide produced by digestion with endopeptidase LysC could be unequivocally determined by tandem mass spectroscopy. Together, these results show that bovine cystatin C has 118 residues, in contrast with 110-112 residues reported previously, and has an N-terminal region analogous to that of human cystatin C. This region presumably is of similar importance for tight binding of target proteinases as in the human inhibitor.

Cloning of a putative G-protein-coupled receptor from Arabidopsis thaliana

We have cloned and characterized a cDNA from Arabidopsis thaliana that most likely encodes a novel member of the vast superfamily of G-protein-coupled receptor proteins (GPCRs). By taking advantage of amino acid sequence similarities between plant expressed sequence tags (ESTs) and established G-protein-coupled receptor sequences, a probe was obtained which was used for the screening of an Arabidopsis cDNA library. The cDNA which was found is very infrequently represented in the cDNA library, suggesting a low and/or spatially restricted expression. A region of the translated sequence of the cDNA shows the highest similarity to cAMP receptors from the slime mold Dictyostelium discoideum. The same region is also similar to that in members of the animal calcitonin family of receptors. Another region of the putative receptor, however, is similar to sequences of serotonin receptors and other receptors of the so-called rhodopsin family of GPCRs. The rhodopsin family has numerous members in higher vertebrate species. Alignments and phylogenetic analyses of the regions of similarity yielded results in accordance with other evolutionary considerations. Our cDNA thus occurred on a distinct major branch in relation to the rest of the rhodopsin family. In relation to the calcitonin family, our cDNA and cAMP receptors occurred together on a distinct major branch but appear to have diverged from each other shortly after their divergence from the rest of the calcitonin family. Other features further argue for a tentative identification of it as a GPCR. It displays seven discrete and strongly predicted transmembrane domains when analyzed in hydropathy plots. The preferred orientation is with the amino terminus towards the outside. It has one Cys residue in extracellular loop 1 and another in extracellular loop 2. Cys residues in these loops are known to form disulfide bridges in many other GPCRs. Finally, it has several fully conserved amino acids that belong to the most conserved in previously known GPCRs, that occur in the above regions of similarity.

Aberrantly expressed cytokeratin 1, a tumor-associated autoantigen in papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is a somewhat puzzling disease, combining a propensity to metastasize with an indolent clinical course. The often pronounced T cell-dominated inflammatory infiltrate seen in PTC tumors has prompted us to search for signs of a tumor-induced immune response. In previous studies, we have demonstrated large tumor-specific deposits of IgG and complement in PTC tissue and isolated a putative target antigen. This investigation examines the presence of autoantibodies to cytokeratin 1, a high m.w. cytokeratin normally expressed only in suprabasal keratinocytes, in the serum and tumor tissue of PTC patients. Using immunoprecipitation and Western blot, cytokeratin 1-reactive autoantibodies were demonstrated in 80% of the PTC sera tested, and tumor-derived antibodies were shown to precipitate cytokeratin 1. Using immunohistochemistry, cytokeratins 1 and 10 were found in a large proportion of PTC tumors (39/44) but were absent from normal thyrocytes of most PTC-bearing glands. Our results indicate that this protein is expressed aberrantly in neoplastic cells and is immunogenic in this context.

Regulation of the wound-induced myrosinase-associated protein transcript in Brassica napus plants

Two slightly differing cDNA clones corresponding to the wound-inducible form of a previously characterized seed myrosinase-associated protein (MyAP) have been isolated from Brassica napus L. The transcripts corresponding to the induced MyAP (iMyAP) were found to be developmentally regulated in various vegetative organs. Both young and old leaves exhibited wound-inducible iMyAP expression. Furthermore, in the young plant, wounding resulted in a systemic increase in leaves located both acropetally and basipetally to the wounded leaf. Also, the iMyAP transcripts were induced by methyl jasmonate, jasmonic acid and abscisic acid. The different inductions could be antagonized by salicylic acid. A general responsiveness in methyl-jasmonate-treated leaves was demonstrated by in situ hybridization. No effect on the amount of iMyAP transcript was detected after feeding the plants with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. The similarity between MyAP and a lipase from Arabidopsis thaliana indicated a possible function in liberating acylated glucosinolates from their acyl group, thereby making them available for hydrolysis by the myrosinase enzymes. We also report on a reduction in the amount of myrosinase transcripts derived from the vegetatively expressed MB-gene family after treatment with exogenously applied salicylic acid or abscisic acid.

Tissue distribution of human gp330/megalin, a putative Ca(2+)-sensing protein

We used riboprobes and monoclonal antibodies to characterize tissue distribution of the human 550-kD homologue to gp330/megalin, primarily identified in the rat kidney. Human gp330/megalin mRNA and protein are readily identified in human parathyroid cells, placental cytotrophoblasts, kidney proximal tubule cells, and epididymal epithelial cells. The immunoreactivity is found on the surface of the cells and is heterogeneously downregulated in parathyroid hyperplasia and adenomas. Cells of the proximal kidney tubule and epididymis express the protein on their luminal aspect. Moreover, the protein is expressed in Type II pneumocytes, mammary epithelial and thyroid follicular cells, and the ciliary body of the eye. Sequence analysis of cDNA fragments, obtained by RT-PCR, revealed identical nucleotide sequences in parathyroid, kidney, placenta, epididymis, and lung. Immunohistochemistry for parathyroid hormone-related protein (PTHrP) revealed partial co-expression with human gp330/megalin in parathyroid, placenta, and mammary gland. The findings substantiate human gp330/megalin expression in a variety of human tissues expected to possess calcium-sensing functions. It may constitute a protein of utmost importance to adult and fetal calcium homeostasis, although other important functions may also be coupled to this exceptionally large protein with highly restricted tissue distribution.

Myrosinase-binding proteins are derived from a large wound-inducible and repetitive transcript

Several non-myrosinase proteins have been found in association with some of the myrosinases extracted from rape (Brassica napus) seed. Most of these proteins seemed to belong to a large family of proteins ranging in size over approximately 30-110 kDa, namely the myrosinase-binding protein (MBP) family. Potentially all of these MBPs might be derived from a single large precursor, encoded by a 3.3-kb transcript. This transcript coded for a 99-kDa glycine-rich protein with a highly repetitive structure. The mature 50-kDa and 52-kDa MBP amino-terminal was located 255 amino acids from the putative initiation methionine. Also, a more divergently related transcript, the protein product of which was unknown, has been cloned. However, the largest open reading frame suggested a proline-rich protein. While this transcript seemed to be expressed predominantly in seeds, the MBP transcripts were expressed in several tissues and also exhibited a responsiveness to wounding and methyl jasmonate. Both proteins exhibited significant similarities to lectins from Artocarpus integer and from Maclura pomifera.

Structural comparison of the precursor and the mature form of napin, the 2S storage protein in Brassica napus

The 2S storage protein napin from Brassica napus var. L. is synthesised as a precursor protein at the endoplasmic reticulum and transported along a gradient of decreasing pH to the vacuole, where two propeptides are removed to produce mature napin. The structures of pronapin expressed in insect cells and mature napin from rape seed were characterised. Limited proteolysis with several endoproteases cleaved primarily in the propeptides, suggesting that the propeptides are exposed to the exterior of the protein. Immunological comparison in parallel with circular dichroic spectrometry, both at neutral and acid pH, indicated that the propeptides had only a minor influence on the conformation of the regions of the molecule that correspond to mature napin.

Functional dissection of a napin gene promoter: identification of promoter elements required for embryo and endosperm-specific transcription

The promoter region (-309 to +44) of the Brassica napus storage protein gene napA was studied in transgenic tobacco by successive 5' as well as internal deletions fused to the reporter gene GUS (beta-glucuronidase). The expression in the two main tissues of the seed, the endosperm and the embryo, was shown to be differentially regulated. This tissue-specific regulation within the seed was found to affect the developmental expression during seed development. The region between -309 to -152, which has a large effect on quantitative expression, was shown to harbour four elements regulating embryo and one regulating endosperm expression. This region also displayed enhancer activity. Deletion of eight bp from position -152 to position -144 totally abolished the activity of the napA promoter. This deletion disrupted a cis element with similarity to an ABA-responsive element (ABRE) overlapping with an E-box, demonstrating its crucial importance for quantitative expression. An internal deletion of the region -133 to -120, resulted in increased activity in both leaves and endosperm and a decreased activity in the embryo. Within this region, a cis element similar to the (CA)n element, found in other storage protein promoters, was identified. This suggest that the (CA)n element is important for conferring seed specificity by serving both as an activator and a repressor element.

The multiple forms of starch-branching enzyme I in Solanum tuberosum

Western blot analysis showed the presence of three forms of starch-branching enzyme (SBE), with apparent molecular masses of 103, 97 and 80 kDa, in extracts of leaves and stored tubers of Solanum tuberosum. The 80-kDa form was absent in extracts of fresh tuber. Active 80-kDa enzyme was partially purified from stored tubers and sequence analysis showed that it, similar to the two larger enzyme forms, was an SBE-I isoform. Limited proteolysis of isolated 103-kDa SBE-I under native conditions removed approximately 200 amino acid residues from the carboxy terminus. A stable intermediate with an apparent molecular mass of approximately 80 kDa was formed. Since the 80-kDa form displayed full enzymatic activity and its circular-dichroism spectrum did not differ significantly from that of the 103-kDa enzyme, the carboxy-terminal portion of the enzyme was suggested to have an extended, unordered structure and therefore to be easily accessible to proteolysis. A cDNA sequence encoding a mature SBE-I was amplified from tuber mRNA of S. tuberosum by means of PCR. The 3' end of this sequence differed significantly from that of previously published data. PCR amplification and DNA sequencing of the 3' ends of the sbeI gene showed that four sbeI alleles exist in the cultivar studied. Two of these four alleles, sbeia and sbeIb, had slightly longer 3' ends compared with the other two, sbeIc and sbeId. The difference between the two groups of alleles was due to a partial deletion in sbeIc and sbeId of a segment duplicated in all alleles. All four alleles were expressed in leaf and tuber.

Identification of a 35 kD tumor-associated autoantigen in papillary thyroid carcinoma

Despite its tendency to metastasize and grow multifocally, papillary thyroid carcinoma (PTC), the most common endocrine malignancy, usually displays an indolent clinical course. Although this behavior probably reflects the inherent low growth potential of PTC cells, it has been postulated that the striking inflammatory reaction often present in PTC represents the activation of a protective, tumor-induced immune response. In a recent immunohistochemical study, we reported that immunoglobulin (IgG) and complement (C3d, C4d and C5) are specifically deposited in PTC tumor tissue. Endeavors were then made to isolate and identify tumor-associated antigens. Immunoprecipitation employing the serum and tumor tissue of PTC patients produced two bands by SDS-PAGE, at approximately 34.5 and 35 kD, which were not present in normal thyroid tissue. Three tryptic peptides of the 35 kD band were sequenced, identifying it as a fragment of cytokeratin 1, a structural protein not normally expressed in the thyroid. The results indicate a tumor-specific antibody response against an aberrantly expressed protein in PTC.

Sequence analysis and regulation of a gene encoding a cuticle-degrading serine protease from the nematophagous fungus Arthrobotrys oligospora

The nematode trapping fungus Arthrobotrys oligospora produces an extracellular serine protease (designated PII) that immobilizes free-living nematodes in bioassays and hydrolyses proteins of the nematode cuticle. Peptides were isolated from PII and partly sequenced. Three internal peptide sequences were used to design synthetic oligonucleotides, which allowed the subsequent isolation of the gene encoding PII from a genomic library. The deduced amino acid sequence indicated that PII is synthesized as a preproenzyme containing the mature enzyme, a signal sequence and a propeptide that are removed before the enzyme is secreted into the medium. The primary sequence of PII displayed a high degree of similarity with several other serine proteases of ascomycetes belonging to the subtilisin family. Northern analysis demonstrated that PII was expressed when the fungus was starved of nitrogen and carbon and that the expression was significantly stimulated by the addition to the medium of various soluble and insoluble proteins, including fragments of nematode cuticle. The levels of the mRNA as well as the proteolytic activity of PII were repressed in the presence of more easily metabolized forms of nitrogen (including ammonia, nitrate and amino acids) or glucose. The activity of the enzyme was almost completely inhibited by the peptide Phe-Val, as well as by the amino acid Phe, without a corresponding decrease in mRNA level. Notably, peptides with similar structures are known to be secreted by the host (nematode) and to stimulate the production of infection structures (traps) of the fungus.

Cloning and sequencing of human gp330, a Ca(2+)-binding receptor with potential intracellular signaling properties

We present here the complete primary structure of human gp330, the human variant of the principal kidney autoantigen causing Heymann membranous glomerulonephritis in rats. The deduced 4655 amino acid residues give a calculated molecular mass of 519636 Da for the mature protein and consists of a probable 25-amino-acid N-terminal signal peptide sequence, an extracellular region of 4398 amino acids, a single transmembrane-spanning domain of 23 amino acids, and an intracellular C-terminal region of 209 amino acid residues. Three types of cysteine-rich repeats characteristic of the low density lipoprotein receptor (LDLR) superfamily are present in human gp330. In the extracellular region, there are a total of 36 LDLR ligand-binding repeats, comprising four distinct domains, 16 growth factor repeats separated by eight YWTD spacer regions, and one epidermal growth factor-like repeat. No consensus cleavage sequence for the processing endoprotease furin is detected in human gp330. The intracellular tail contains not only two copies of the F(X)NPXY coated-pit mediated internalization signal characteristic of LDLR superfamily members, but also intriguing and potentially functional motifs including several Src-homology 3 recognition motifs, one Src-homology 2 recognition motif for the p85 regulatory subunit of phosphatidylinositol 3-kinase, and additional sites for protein kinase C, casein kinase II and cAMP-/cGMP-dependent protein kinase. There is approximately 77% amino acid identity between human and rat gp330 with minor differences between the extracellular and intracellular regions. Recently gp330 has been implicated in Ca2+ regulation in the parathyroid, the placenta, and the renal tubule, but its overall physiological and pathological role still remains uncertain.

Molecular characterization of a saline-soluble lectin from a parasitic fungus. Extensive sequence similarities between fungal lectins

It has been proposed that the interactions between several parasitic and pathogenic fungi and their hosts are mediated by soluble lectins present in the fungus. We have cloned and analyzed a gene encoding such a lectin (AOL) from the nematophagous fungus Arthrobotrys oligospora (deuteromycete). The deduced primary structure of the AOL gene displayed an extensive similarity (identity 46.3%) to that of a gene encoding a lectin (ABL) recently isolated from the mushroom Agaricus bisporus (basidiomycete), but not to any other fungal, microbial, plant or animal lectins. The similarities between AOL and ABL were further demonstrated by the observation that an antibody specific for AOL cross-reacted with ABL. Together with data showing that AOL has a binding specificity that is similar to that of ABL [Rosen, S., Bergström, J., Karlsson, K.-A. & Tunlid, A. (1996) Eur. J. Biochem. 238, 830-837], these results indicate that AOL and ABL are members of a novel family of saline soluble lectins present in fungi. Southern blots indicated that there is only one AOL gene in the genome encoding a subunit (monomer) of the lectin. The primary structure of AOL did not show the presence of a typical N-terminal signal sequence. Comparison of the deduced primary structure with the molecular mass of AOL as determined by electrospray mass spectrometry (16153 Da), indicated that AOL has an acetylated N-terminal but no other post-translational modifications, and that a minor isoform is formed by deamidation. Circular dichroism (CD) spectroscopy suggested that the secondary structure of AOL contains 34% beta-sheets, 21% alpha-helix, and 45% turns and coils.

A wound- and methyl jasmonate-inducible transcript coding for a myrosinase-associated protein with similarities to an early nodulin

Myrosinase is regarded as a defense-related enzyme in the Brassicaceae and is capable of hydrolyzing glucosinolates into various compounds, some of which are toxic. Several myrosinase isoenzymes exist, and some of them have been found in association with nonmyrosinase proteins. One of these associated proteins, myrosinase-associated protein (MyAP), was purified from seeds of Brassica napus both in complexes with myrosinase and in a free form. MyAP is a glycosylated, 40-kD protein with at least one intramolecular disufide bridge. A monoclonal anti-MyAP antibody precipitated myrosinase activity from B. napus seed extracts and in these complexes both a 65- and a 70-kD myrosinase were present. The subsequent cloning and analysis revealed the existence of a gene family encoding MyAP or MyAP-related protein and that transcripts corresponding to MyAP in nonwounded plants are found predominantly in seeds. At least some members of the gene family exhibited responsiveness toward wounding and methyl jasmonate vapor. MyAP displayed considerable similarity to an early nodulin (ENOD8) from Medicago sativa and to a proline-rich protein (APG), described as another specific, from Arabidopsis thaliana and B. napus. Similarity to expressed sequence tags from both A. thaliana and Oryza sativa has also been found.

Disruption of an overlapping E-box/ABRE motif abolished high transcription of the napA storage-protein promoter in transgenic Brassica napus seeds

The storage protein napin is one of the major protein components of Brassica napus L. (oilseed rape) seeds. To investigate the transcriptional regulation of the napin promoter, different constructs of the napin gene napA promoter were fused to the Escherichia coli uidA gene and transformed into B. napus. A-152-bp promoter construct directed a strong expression of the marker gene in mature seeds. The 5' deletion of an additional 8 completely abolished this activity. This deletion disrupted sequence motifs that are similar to an E-box, (CA decreases NNTG) and an ABRE (CGCCA decreases CGTGTCC) element (identify is indicated by bold face). Further, internal deletion of a segment corresponding to -133 to -121 caused an eightfold reduction in the activity of the -152 construct. This region contains an element, CAAACAC, conserved in many storage-protein gene promoters. These results imply that the E-box/ABRE-like sequence is a major motif of the napA promoter and suggest that the CAAACAC sequence is important for high activity of the napA promoter. Similar results have been obtained by analysing some of the constructs in transgenic tobacco, suggesting that many of the cis-elements in the napA promoter are conserved, at least in dicotyledonous species.