Gene note. Isolation of a cDNA corresponding to a low temperature- and ABA-responsive gene encoding a putative glycine-rich RNA-binding protein in Solanum commersonii

A cDNA encoding a putative RNA-binding glycine-rich protein, SCRGP-1, was isolated from the wild potato species Solanum commersonii. The amino acid sequence of the deduced protein revealed that the protein contains a consensus RNA-binding domain and has a glycine-rich carboxy-terminal domain. The corresponding gene is induced by low temperature, ABA, wounding, and drought in both Solanum commersonii and Solanum tuberosum. The response of this putative RNA-binding protein gene to low temperature and ABA treatments in Solanum sp. suggests that the SCRGP-1 protein might participate in the adaptation process leading to increased freezing tolerance.     

hnRNP G: sequence and characterization of a glycosylated RNA-binding protein.

The autoantigen p43 is a nuclear protein initially identified with autoantibodies from dogs with a lupus-like syndrome. Here we show that p43 is an RNA-binding protein, and identify it as hnRNP G, a previously described component of heterogeneous nuclear ribonucleoprotein complexes. We demonstrate that p43/hnRNP G is glycosylated, and identify the modification as O-linked N-acetylglucosamine. A full-length cDNA clone for hnRNP G has been isolated and sequenced, and the predicted amino acid sequence for hnRNP G shows that it contains one RNP-consensus RNA binding domain (RBD) at the amino terminus and a carboxyl domain rich in serines, arginines and glycines. The RBD of human hnRNP G shows striking similarities with the RBDs of several plant RNA-binding proteins.     

Characteristics and epitope mapping of a cloned human autoantigen La

The La (SS-B) polypeptide is a ribonucleoprotein against which high titer antinuclear antibodies (ANA) react in the human autoimmune disease primary Sj?gren's syndrome. To identify the autoepitopes with which the ANA anti-La (anti-SS-B) reacts, we isolated a 1.4-kb cDNA clone for La from a lambda gt10 library made from a human Burkitt's cell line. This clone contained an open reading frame of 1065 bp, encoding a 40.1-kDa polypeptide that corresponded to the carboxyl-terminal end of the La protein. The predicted polypeptide sequence of the recombinant protein was highly charged and unrelated to any previously published sequence. We also compared this clone to a previously published cDNA sequence for La and demonstrated significant differences, particularly that the open reading frame in our cDNA continued for 926 additional bases 3' to a putative termination codon in the previously reported sequence. The recombinant La protein was expressed in Escherichia coli and tested for reactivity with 200 sera containing ANA of various specificities. Only the sera containing anti-La antibodies reacted with the cloned La. By expressing subclones of the La cDNA as fusion proteins with beta-galactosidase, we have localized at least one epitope for the binding of anti-La antibodies to the carboxyl-terminal 103 amino acids of the La protein. No anti-La binding could be demonstrated to the region of the La protein that had previously been predicted to contain an autoepitope for the binding of anti-La (SS-B) antibodies. Studies of cloned autoepitopes could provide important clues to the role ANA play in disease and lead to targeted intervention in the treatment of primary Sj?gren's syndrome.     

Identification and characterization of a novel protein that regulates RNA-protein interaction

In a previous study [Nachaliel et al., 1993], we identified an RNA-binding protein (RBP) in FTO-2B rat hepatoma cells whose activity was stimulated upon the dissociation of a protein factor. We report in this article that the RBP is a complex protein of about 400 kDa, composed of RNA-binding subunit(s) (RBS), and regulatory subunit(s) (RS). We purified the RS to near-homogeneity (Mr approximately 25,000) and determined the amino acid sequence of a peptide derived from RS. On the basis of this sequence information, the cDNA for RS was obtained. Recombinant RS protein expressed in Escherichia coli had the capacity to bind RBS and inhibit its RNA-binding activity. The cDNA contains the complete coding sequence because the recombinant protein has the same electrophoretic mobility as that of the native RS in SDS-polyacrylamide gels. Sequence comparison showed that RS is almost identical to DJ-1, a recently discovered protein with an oncogenic potential, and CAP1, a rat sperm protein. However, the protein does not contain any known motifs that can provide a clue as to its exact function. Indirect immunofluorescence analyses showed that in addition to the cytoplasm, where RS is associated with microtubular filaments, the polypeptide is localized to the cell nucleus. The possible role of RS is discussed.     

Phosphorylation of a chloroplast RNA-binding protein changes its affinity to RNA.

An RNA-binding protein of 28 kDa (28RNP) was previously isolated from spinach chloroplasts and found to be required for 3' end-processing of chloroplast mRNAs. The amino acid sequence of 28RNP revealed two approximately 80 amino-acid RNA-binding domains, as well as an acidic- and glycine-rich amino terminal domain. Upon analysis of the RNA-binding properties of the 'native' 28RNP in comparison to the recombinant bacterial expressed protein, differences were detected in the affinity to some chloroplastic 3' end RNAs. It was suggested that post-translational modification can modulate the affinity of the 28RNP in the chloroplast to different RNAs. In order to determine if phosphorylation accounts for this post-translational modification, we examined if the 28RNP is a phosphoprotein and if it can serve as a substrate for protein kinases. It was found that the 28RNP was phosphorylated when intact chloroplasts were metabolically labeled with [32P] orthophosphate, and that recombinant 28RNP served as an excellent substrate in vitro for protein kinase isolated from spinach chloroplasts or recombinant alpha subunit of maize casein kinase II. The 28RNP was apparently phosphorylated at one site located in the acidic domain at the N-terminus of the protein. Site-directed mutagenesis of the serines in that region revealed that the phosphorylation of the protein was eliminated when serine number 22 from the N-terminus was changed to tryptophan. RNA-binding analysis of the phosphorylated 28RNP revealed that the affinity of the phosphorylated protein was reduced approximately 3-4-fold in comparison to the non-phosphorylated protein. Therefore, phosphorylation of the 28RNP modulates its affinity to RNA and may play a significant role in its biological function in the chloroplast.     

皖南尖吻蝮蛇毒中类去整合蛋白/富含半胱氨酸两结构域cDNA的克隆和表达

为了探讨出血毒金属蛋白酶结构功能关系 ,通过 RT- PCR方法 ,从皖南尖吻蝮蛇( Agkistrodon acutus)毒腺总 RNA中扩增得到编码 P- 型出血毒金属蛋白酶的完整类去整合蛋白和富含半胱氨酸两个结构域 c DNA( AA/DC) .它全长 964bp的 c DNA,开放阅读框架编码 2 1 6个氨基酸残基 ,序列比较分析表明它同来自 Bothrops jararaca的 jararhagin- C、来自 Crotalus atrox的 catrocollastatin- C有很高的同源性 .在类去整合蛋白结构域中 ,Ser- Glu- Cys- Asp( SECD)代替了去整合蛋白中相应部位的 Arg- Gly- Asp( RGD)三肽序列 .将编码区基因克隆入 p GEX- 2 T载体中 ,转化大肠杆菌 TG- 1 ,用 IPTG诱导表达 ,表达产物具有抑制胶原诱导的血小板凝集活性 ,但不抑制ADP诱导的血小板凝集 .该研究为进一步阐述蛇毒金属蛋白酶结构功能关系和药物开发奠定了基础 .     

RNA-binding activity of hepatitis delta antigen involves two arginine-rich motifs and is required for hepatitis delta virus RNA replication.

Hepatitis delta antigen (HDAg) is an RNA-binding protein with binding specificity for hepatitis delta virus (HDV) RNA (J. H. Lin, M. F. Chang, S. C. Baker, S. Govindarajan, and M. M. C. Lai, J. Virol. 64:4051-4058, 1990). By amino acid sequence homology search, we have identified within its RNA-binding domain two stretches of an arginine-rich motif (ARM), which is present in many prokaryotic and eukaryotic RNA-binding proteins. The first one is KERQDHRRRKA and the second is EDEKRERRIAG, and they are separated by 29 amino acids. Deletion of either one of these ARM sequences resulted in the total loss of the in vitro RNA-binding activity of HDAg. Thus, HDAg is different from other RNA-binding proteins in that it requires two ARM-like sequences for its RNA-binding activity. Replacement of the spacer sequence between the two ARMs with a shorter stretch of sequence also reduced RNA binding in vitro. Furthermore, site-specific mutations of the basic amino acid residues in both ARMs resulted in the total loss or reduction of RNA-binding activity. The biological significance of the RNA-binding activity was studied by examining the trans-activating activity of the RNA-binding mutants. The plasmids expressing HDAgs with various mutations in the RNA-binding motifs were cotransfected with a replication-defective HDV dimer cDNA construct into COS cells. It was found that all the HDAg mutants which had lost the in vitro RNA-binding activity also lost the ability to complement the defect of HDV RNA replication. We conclude that the trans-activating function of HDAg requires its binding to HDV RNA.     

Cloning, expression, and characterization of a cDNA encoding snake venom metalloprotease

A cDNA clone, MT-c, encoding metalloprotease was isolated from snake (Agkistrodon halys brevicadus) venom gland cDNA library. Deduced amino acid sequence indicated that MT-c is composed of a signal sequence, amino-terminal propeptide, a central metalloprotease domain, and a Lys-Gly-Asp (KGD) disintegrin domain. The partial cDNA encoding metalloprotease and disintegrin domain was subcloned and expressed in E. coli. The expressed MT-c protein was purified and successfully refolded into functional form retaining the enzyme activity. Analyses of the purified recombinant protease activity revealed that the enzyme hydrolyzes extracellular matrix proteins including type I gelatin, type IV and type V collagen, while type I, II, III collagens and fibronectin were insensitive to the proteolytic digestion. The recombinant enzyme was also able to degrade fibrinogen by specifically cleaving A alpha chain of the protein.     

The primary structure of rat ribosomal protein L12

The covalent structure of the rat 60S subunit protein L12 which is a component of the ribosomal elongation factor binding domain was deduced from the sequence of nucleotides in a recombinant cDNA and confirmed from the NH2-terminal amino acid sequence of the protein. L12 has 165 amino acids and a molecular weight of 17,834. Hybridization of the cDNA to digests of nuclear DNA suggests that there are 11-13 copies of the L12 gene. The mRNA for the protein is about 800 nucleotides in length. Rat L12 is homologous to Saccharomyces cerevisiae L15. The cDNA contains the highly repetitive DNA sequence, R.dre.1, in the 3' noncoding region.     

A new Arabidopsis nucleic-acid-binding protein gene is highly expressed in dividing cells during development

An Arabidopsis thaliana cDNA encoding a new RNA-binding protein (RBP37) was cloned from a silique cDNA library. The predicted amino acid sequence corresponds to a RBP containing two RNA recognition motifs (RRM) and a basic domain. An affinity for nucleic acids was confirmed in binding assays using in vitro synthesised AtRBP37 protein. In situ hybridisation experiments on sections of flowers and siliques showed expression only in growing organs: gynoecium, petals, filaments and during early-embryogenesis expression is located in the embryo proper and the suspensor up to late heart stage. Expression is not detected in the embryo during maturation.This results suggests an expression pattern correlated with dividing cells.     

A low-temperature-responsive gene from barley encodes a protein with single-stranded nucleic acid-binding activity which is phosphorylated in vitro

A low-temperature-responsive gene, blt 801, isolated from a winter barley (Hordeum vulgare L.) cDNA library prepared from leaf meristematic tissue, was sequenced. The deduced amino acid sequence predicts a glycine-rich RNA-binding protein (GR-RNP) which was homology to stress-responsive GR-RNPs from several other plant species. BLT 801 is a two-domain protein, the amino-terminal domain comprises a consensus RNA-binding domain similar to that found in many eukaryotic genes and the carboxy-terminal domain is extremely glycine-rich (68.5% glycine). Blt 801 mRNA also accumulates in response to the phytohormone abscisic acid. The protein encoded by blt 801 has been produced as a recombinant fusion protein using a bacterial expression vector. The fusion protein, a chimaera of glutathione S-transferase and BLT 801, has been used in studies to determine nucleic acid binding and other characteristics. Binding studies with single-stranded nucleic acids show that BLT 801 has affinity for homoribopolymers G, A and U but not C, it also binds to single-stranded DNA and selects RNA molecules containing open loop structures enriched in adenine but low in cytosine. BLT 801 has a consensus motif for phosphorylation by cAMP protein kinase (PKA) at the junction between the two domains which can be phosphorylated by PKA in vitro and which, by analogy to animal studies, may have significance for controlling enzyme function.     

The human RD protein is closely related to nuclear RNA-binding proteins and has been highly conserved

We have isolated cDNA clones encoding the human RD protein, which is closely related to several known nuclear RNA-binding proteins. The RD protein contains a 60-amino acid (aa) tract almost entirely of alternating basic and acidic aa, (RD)_n, primarily arginine (Arg; R) and aspartic acid (Asp; D). The protein also contains an ‘RNP sequence domain’. Arg-rich tracts and the RNP sequence domain are both features of nuclear RNA-binding proteins. However, we have been unable to detect RNA-binding by the human RD protein. The very strong evolutionary conservation of the mammalian RD protein as sequence suggests that it plays an important role in the cell.     

Porcine pyridoxal kinase: c-DNA cloning, expression and confirmation of its primary sequence

Porcine brain pyridoxal kinase has been cloned. A 1.2 kilo-based cDNA with a 966-base pair open reading frame was determined from a porcine brain cortex cDNA library using PCR technique. The DNA sequence was shown to encode a protein of 322 amino acid residues with a molecular mass of 35.4 kDa. The amino acid sequence deduced from the nucleotide sequence of the cDNA was shown to match the partial primary sequence of pyridoxal kinase. Expression of the cloned cDNA in E. coli has produced a protein which displays both pyridoxal kinase activity and immunoreactivity with monoclonal antibodies raised against natural enzyme from porcine brain. With respect to the physical properties, it is shown that the recombinant protein exhibits identical kinetic parameters with the pure enzyme from porcine brain. Although the primary sequence of porcine pyridoxal kinase has been shown to share 87% homology with the human enzyme, we have shown that the porcine enzyme carries an extra peptide of ten amino acid residues at the N-terminal domain.     

Molecular cloning and characterization of coclaurine N-methyltransferase from cultured cells of Coptis japonica.

S-adenosyl-L-methionine:coclaurine N-methyltransferase (CNMT) converts coclaurine to N-methylcoclaurine in isoquinoline alkaloid biosynthesis. The N-terminal amino acid sequence of Coptis CNMT was used to amplify the corresponding cDNA fragment and later to isolate full-length cDNA using 5'- and 3'-rapid amplification of cDNA ends (RACE). The nucleotide sequence and predicted amino acid sequence showed that the cDNA encoded 358 amino acids, which contained a putative S-adenosyl-L-methionine binding domain and showed relatively high homology to tomato phosphoethanolamine-N-methyltransferase. A recombinant protein was expressed in Escherichia coli, and its CNMT activity was confirmed. Recombinant CNMT was purified to homogeneity, and enzymological characterization confirmed that Coptis CNMT has quite broad substrate specificity, i.e. not only for 6-O-methylnorlaudanosoline and norreticuline but also for 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline. The evolution of N-methyltransferases in secondary metabolism is discussed based on sequence similarity.