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Novel pre-C/C gene mutants of hepatitis B virus in chronic active hepatitis: naturally occurring escape mutants.

We have analysed serum samples taken from hepatitis B virus (HBV) e antigen (HBeAg)-positive and HBeAg-negative chronic active hepatitis (CAH) patients by PCR using primers spanning the pre-core/core (C) and pre-S1/S2 ORFs. Nucleotide sequence analysis showed that among 18 HBV-infected CAH patients, 11 had virus with a G to A mutation (nucleotide 1896; leading to the formation of a stop codon) and one patient also had virus with an additional G to A mutation three nucleotides downstream (nucleotide 1899). HBV from three patients that were HBeAg-negative showed a 1 bp deletion at nucleotide 1937, causing pre-termination of the C gene. Mutation frequencies in the sequences identified as coding for cytotoxic T lymphocyte epitopes, B cell epitopes, CD4+ helper T cell epitopes and arginine-rich regions of the HBV C peptide were investigated. Mutations were more frequently identified in these regions, suggesting that the mutations might have been selected as a result of immune responses.

Adolescent↗

A family 26 mannanase produced by Clostridium thermocellum as a component of the cellulosome contains a domain which is conserved in mannanases from anaerobic fungi.

Cellulosomes prepared by the cellulose affinity digestion method from Clostridium thermocellum culture supernatant hydrolysed carob galactomannan during incubation at 60 degrees C and pH 6.5. A recombinant phage expressing mannanase activity was isolated from a library of C. thermocellum genomic DNA constructed in lambdaZAPII. The cloned fragment of DNA containing a putative mannanase gene (manA) was sequenced, revealing an ORF of 1767 nt, encoding a protein (mannanase A; Man26A) of 589 aa with a molecular mass of 66816 Da. The putative catalytic domain (CD) of Man26A, identified by gene sectioning and sequence comparisons, displayed up to 32% identity with other mannanases belonging to family 26. Immediately downstream of the CD and separated from it by a short proline/threonine linker was a duplicated 24-residue dockerin motif, which is conserved in all C. thermocellum cellulosomal enzymes described thus far and mediates their attachment to the cellulosome-integrating protein (CipA). Man26A consisting of the CD alone (Man26A") was hyperexpressed in Escherichia coli BL21(DE3) and purified. The truncated enzyme hydrolysed soluble and insoluble mannan, displaying a temperature optimum of 65 degrees C and a pH optimum of 6.5, but exhibited no activity against other plant cell wall polysaccharides. Antiserum raised against Man26A" cross-reacted with a polypeptide with a molecular mass of 70000 Da that is part of the C. thermocellum cellulosome. A second variant of Man26A containing the N-terminal segment of 130 residues and the CD (Man26A") bound to ivory-nut mannan and weakly to soluble Carob galactomannan and insoluble cellulose. Man26A" consisting of the CD alone did not bind to these polysaccharides. These results indicate that the N-terminal 130 residues of mature Man26A may constitute a weak mannan-binding domain. Sequence comparisons revealed a lack of identity between this region of Man26A and other polysaccharide-binding domains, but significant identity with a region conserved in the three family 26 mannanases from the anaerobic fungus Piromyces equi.

Animals↗

Molecular cloning and characterization of genes for Shigella sonnei form I O polysaccharide: proposed biosynthetic pathway and stable expression in a live salmonella vaccine vector.

The gene region for biosynthesis of Shigella sonnei form I O polysaccharide (O-Ps) and flanking sequences, totaling >18 kb, was characterized by deletion analysis to define a minimal construct for development of Salmonella-based live vaccine vector strains. Lipopolysaccharide (LPS) expression and DNA sequence studies of plasmid deletion derivatives indicated form I O-Ps expression from a 12.3-kb region containing a putative promoter and 10 contiguous open reading frames (ORFs), one of which is the transposase of IS630. A detailed biosynthetic pathway, consistent with the predicted functions of eight of the nine essential ORFs and the form I O-Ps structure, is proposed. Further sequencing identified partial IS elements (i.e., IS91 and IS630) and wzz upstream of the form I coding region and a fragment of aqpZ and additional full or partial IS elements (i.e., IS629, IS91, and IS911) downstream of this region. The stability of plasmid-based form I O-Ps expression was greater from low-copy vectors than from high-copy vectors and was enhanced by deletion of the downstream IS91 from plasmid inserts. Both core-linked (i.e., LPS) and non-core-linked (i.e., capsule-like) surface expression of form I O-Ps were detected by Western blotting and silver staining of polyacrylamide gel electrophoresis-separated Shigella and Escherichia coli extracts. However, salmonellae, which have a core that is chemically dissimilar to that of shigellae, expressed only non-core-linked surface-associated form I O-Ps. Finally, attenuated Salmonella enterica serovar Typhi live vaccine vector candidates, containing minimal-sized form I operon constructs, elicited immune protection in mice against virulent S. sonnei challenge, thereby supporting the promise of live, oral vaccines for the prevention of shigellosis.

Animals↗

Evidence that the GCN2 protein kinase regulates reinitiation by yeast ribosomes.

The yeast gene GCN4 produces an mRNA that has a long 5' 'untranslated' region containing four small open reading frames (ORFs) preceding the protein coding frame. This configuration suppresses the rate by which GCN4 protein is synthesized. However, translational derepression of the GCN4 mRNA occurs when yeast cells are grown under conditions of amino acid limitation. Such translational derepression requires the GCN2 protein kinase and the presence of the 5' most proximal ORF. In this study we show that a functional coupling between the translation of the first ORF and the amount of the GCN2 protein is responsible for the translational derepression of the GCN4 mRNA. Our evidence suggests that this coupling involves an increase in the ability of 40S ribosomal subunits that have translated the first frame to resume scanning and reinitiate translation at a downstream AUG independently of the base sequence in the intervening region.

Base Sequence↗

High-throughput expression of fusion proteins.

The expression of putative ORFs as fusion proteins can accelerate research greatly. The availability of an epitope tag allows the use of Western blotting as an efficient means to identify useful recombinant plasmids, which can then be used to study protein function. In addition, the epitope tag can be extremely useful in downstream applications such as protein purification, immunolocalization, and immunoprecipitation experiments. The preceding protocols should be applicable to a variety of expression vectors, and should be useful in the identification of functional plasmids. The protocols require no exotic equipment and can be adapted for use in high-throughput transfection assays, protein purification protocols, and immunolocalization studies.

Animals↗

Location, DNA sequence and transcriptional analysis of the DNA polymerase gene of orf virus.

Degenerate oligonucleotides representing conserved regions of various DNA polymerases hybridized to a region located 26 kb from the left end of the orf virus (OV) strain NZ-2 genome. DNA sequence analysis of this region revealed a 3024 bp open reading frame able to encode a protein with 56 percent amino acid identity to the DNA polymerase of vaccinia virus (VAC) and with significant homology to other DNA polymerases. Early transcripts derived from the open reading frame were detected in RNA purified from OV-infected cells, and 5' ends were mapped to a region 8-19 nt downstream from an A/T-rich sequence that resembles VAC early promoters. Unlike the VAC gene, the OV DNA polymerase makes almost exclusive use of G/C coding options. Attempts to substitute the activity of the OV DNA polymerase for its VAC counterpart were unsuccessful. This may indicate that the OV DNA polymerase is incompatible with VAC accessory proteins.

Amino Acid Sequence↗

Identification and characterization of the bovine herpesvirus 5 US4 gene and gene products.

The BHV-5 strain N569 (BHV-5/N569) homolog to the BHV-1 US4 gene was sequenced and characterized. RNA analyses showed that a 1.8-kb mRNA which contains the BHV-5/N569 US4 open reading frame initiates 55 nucleotides upstream from the predicted translational start codon and terminates 17 nucleotides downstream from the consensus sequence for polyadenylation. Comparison of the deduced amino acid sequences of the predicted US4 encoded proteins of BHV-5/N569 and BHV-1 strain Schönböken (BHV-1/Schö) revealed 75% identity. An antiserum, raised in rabbits after infection with a BHV-5/N569 US4 ORF expressing recombinant vaccinia virus, specifically precipitated a 65-kDa protein and a diffusely migrating protein species with an apparent molecular mass between 90 and > 240 kDa from the supernatant of BHV-5/ N569 infected cells. Treatment of immmunprecipitated proteins with chondroitinase AC demonstrated that the latter contains glycosaminoglycans. The mobility of the BHV-5/N569 US4 gene products was identical to the BHV-1 US4 ORF encoded glycoprotein G (gG) and glycoproteoglycan G (gpgG; G. M. Keil, T. Engelhardt, A. Karger, and M. Enz. J. Virol. 70, 3032-3038, 1996) and were therefore named BHV-5 gG and BHV-5 gpgG. Immunoprecipitations with sera from BHV-1 infected cattle indicated a type-specific immune response to gG, since these sera failed to react with vaccinia virus-expressed gG-5 but recognized vaccinia virus-expressed gG-1.

Alphaherpesvirinae↗

Exoenzyme S of Pseudomonas aeruginosa is secreted by a type III pathway.

Exoenzyme S is an extracellular ADP-ribosyltransferase of Pseudomonas aeruginosa. Transposon mutagenesis of P. aeruginosa 388 was used to identify genes required for exoenzyme S production. Five Tn5Tc insertion mutants were isolated which exhibited an exoenzyme S-deficient phenotype (388::Tn5Tc 469, 550, 3453, 4885, and 5590). Mapping experiments demonstrated that 388::Tn5Tc 3453, 4885, and 5590 possessed insertions within a 5.0 kb EcoRI fragment that is not contiguous with the exoenzyme S trans-regulatory operon. 388::Tn5Tc 469 and 550 mapped to a region downstream of the trans-regulatory operon which has been previously shown to contain a promoter region that is co-ordinately regulated with exoenzyme S synthesis. Nucleotide sequence analysis of a 7.2 kb region flanking the 388::Tn5Tc 469 and 550 insertions, identified 12 contiguous open reading frames (ORFs). Database searches indicated that the first ORF, ExsD, is unique. The other 11 ORFs demonstrated high homology to the YscB-L proteins of the yersiniae Yop type III export apparatus. RNase-protection analysis of wild-type and mutant strains indicated that exsD and pscB-L form an operon. To determine whether ExoS was exported by a type III mechanism, derivatives consisting of internal deletions or lacking amino- or carboxy-terminal residues were expressed in P. aeruginosa. Deletion analyses indicated that the amino-terminal nine residues are required for ExoS export. Combined data from mutagenesis, regulatory, expression, and sequence analyses provide strong evidence that P. aeruginosa possesses a type III secretion apparatus which is required for the export of exoenzyme S and potentially other co-ordinately regulated proteins.

ADP Ribose Transferases↗

The gene encoding the 17-kDa antigen of Bartonella henselae is located within a cluster of genes homologous to the virB virulence operon.

A Bartonella henselae genomic A library was screened with antiserum generated in mice against live B. henselae. One of the immunoreactive clones expressed a 17-kDa antigen that was characterized previously as an immunodominant protein of B. henselae. Sequence analysis of the recombinant clone, pBHIM-2, revealed that the open reading frame (ORF) encoding the 17-kDa antigen was situated between homologs of virB4 and virB6, two genes that belong to the virB operon. The virB operon has been associated with the transfer of oncogenic T-DNA in Agrobacterium tumefaciens and with secretion of the pertussis toxin in Bordetella pertussis. Downstream of the virB6 gene within pBHIM-2 was a partial open reading frame that was homologous to the virB8 gene. Rescreening of the library by plaque hybridization using probes specific to the 5' and 3' ends of the pBHIM-2 insert resulted in the isolation of recombinant clones containing additional virB genes. Assembly of the sequences obtained from the recombinant clones revealed that eight of the open reading frames encode homologs of the VirB proteins. The homology and colinearity with the virB genes suggest that the gene encoding the 17-kDa antigen is expressed within the virB locus of B. henselae.

Animals↗

A bicistronic subgenomic mRNA encodes both the ORF2 and ORF3 proteins of hepatitis E virus.

Hepatitis E virus replicons containing the neomycin resistance gene expressed from open reading frames (ORFs) 2 and 3 were transfected into Huh-7 cells, and stable cell lines containing functional replicons were selected by constant exposure to G418 sulfate. Northern blot analyses detected full-length replicon RNA and a single subgenomic RNA. This subgenomic RNA, which was capped, initiated at nucleotide 5122 downstream of the first two methionine codons in ORF3 and was bicistronic; two closely spaced methionine codons in different reading frames were used for the initiation of ORF3 and ORF2 translation.

Capsid Proteins↗

Sequence analysis and expression of the aspartokinase and aspartate semialdehyde dehydrogenase operon from rifamycin SV-producing amycolatopsis mediterranei.

A approximately 4.8 kb KpnI fragment, from the upstream region of the methylmalonyl-CoA mutase gene (mutAB) of rifamycin SV-producing Amycolatopsis mediterranei, was cloned and partially sequenced. Codon preference analysis showed three complete ORFs. ORF2 is internal to ORF1, and encodes a polypeptide corresponding to 172 amino acids, whereas ORF1 encodes a polypeptide of 421 amino acids. They were identified as the encoding genes of aspartokinase alpha- and beta-subunits by comparing the amino acid sequences with those in the database. The downstream ORF3, whose start codon was overlapped with the stop codon of both ORF1 and ORF2 by 1 bp, was identified as the aspartate semialdehyde dehydrogenase gene (asd), encoding a polypeptide of 346 amino acids. Subclones containing either the ask gene or the asd gene were constructed, in which the genes could be expressed under Lac promoters. Two subclones could transform E. coli CGSC 5074 (ask-) and E. coli X6118 (asd-) to prototrophy, supporting the functional assignments. Southern hybridisation indicated that the approximately 4.8 kb sequenced region represented a continuous segment in the A. mediterranei chromosome. It is concluded that ask and asd genes are present in an operon in A. mediterranei, and therefore that organisation of these two genes is the same as in most gram-positive bacteria, such as Mycobacteria, Corynebacterium glutamicum and Bacillus subtilis, but is different from Streptomyces akiyoshiensis.

Actinobacteria↗

Pyret, a Ty3/Gypsy retrotransposon in Magnaporthe grisea contains an extra domain between the nucleocapsid and protease domains.

A novel Ty3/Gypsy retrotransposon, named Pyret, was identified in the plant pathogenic fungus Magnaporthe grisea (anamorph Pyricularia oryzae). Pyret-related elements were distributed in a wide range of Pyricularia isolates from various gramineous plants. The Pyret element is 7250 bp in length with a 475 bp LTR and one conceptual ORF. The ORF contains seven nonsense mutations in the reading frame, indicating that the Pyret clone is lightly degenerate. Comparative domain analysis among retroelements revealed that Pyret exhibits an extra domain (WCCH domain) beyond the basic components of LTR retrotransposons. The WCCH domain consists of approximately 300 amino acids and is located downstream of the nucleocapsid domain. The WCCH domain is so named because it contains two repeats of a characteristic amino acid sequence, W-X(2)-C-X(4)-C-X(2)-H-X(3)-K. A WCCH motif-like sequence is found in the precoat protein of some geminiviruses, viral RNA-dependent RNA polymerase and also in an Arabidopsis protein of unknown function. Interestingly, detailed sequence analysis of the gag protein revealed that Pyret, as well as some other chromodomain-containing LTR retrotransposons, displays significant sequence homology with members of the gammaretroviruses (MLV-related retroviruses) in the capsid and nucleocapsid domains. This suggests that chromodomain-containing LTR retrotransposons and gammaretroviruses may share a common ancestor with the gag protein.

Amino Acid Motifs↗

Gill-associated virus of Penaeus monodon prawns: an invertebrate virus with ORF1a and ORF1b genes related to arteri- and coronaviruses.

A 20089 nucleotide (nt) sequence was determined for the 5' end of the (+)-ssRNA genome of gill-associated virus (GAV), a yellow head-like virus infecting Penaeus monodon prawns. Clones were generated from a approximately 22 kb dsRNA purified from lymphoid organ total RNA of GAV-infected prawns. The region contains a single gene comprising two long overlapping open reading frames, ORF1a and ORF1b, of 4060 and 2646 amino acids, respectively. The ORFs are structurally related to the ORF1a and ORF1ab polyproteins of coronaviruses and arteriviruses. The 99 nt overlap between ORF1a and ORF1b contains a putative AAAUUUU 'slippery' sequence associated with -1 ribosomal frameshifting. A 131 nt stem-loop with the potential to form a complex pseudoknot resides 3 nt downstream of this sequence. Although different to the G/UUUAAAC frameshift sites and 'H-type' pseudoknots of nidoviruses, in vitro transcription/translation analysis demonstrated that the GAV element also facilitates read-through of the ORF1a/1b junction. As in coronaviruses, GAV ORF1a encodes a 3C-like cysteine protease domain located between two hydrophobic regions. However, its sequence suggests some structural relationship to the chymotrypsin-like serine proteases of arteriviruses. ORF1b encodes homologues of the 'SDD' polymerase, which among (+)-RNA viruses is unique to nidoviruses, as well as metal-ion-binding and helicase domains. The presence of a dsRNA replicative intermediate and ORF1a and ORF1ab polyproteins translated by a-1 frameshift suggests that GAV represents the first invertebrate member of the Order NIDOVIRALES:

Amino Acid Sequence↗

Streptococcus pyogenes sclB encodes a putative hypervariable surface protein with a collagen-like repetitive structure.

Streptococcus pyogenes is the causative agent in a wide range of diseases of humans of varying severity. During a study scanning the genome sequence of a serotype M1 invasive isolate SF370 for novel surface proteins, an ORF, designated sclB, was identified. The putative protein encoded by sclB contains both a signal peptide and classic Gram-positive wall-associated sequences. Comparison of the sequences of this ORF with those from a number of unrelated isolates demonstrated that sclB encodes a putative surface protein with a variable N-terminal sequence followed by a variable length tract of collagen-like GXY(n) repeats. A further feature of sclB is the presence of CAAAA repeat tracts immediately downstream of the putative start codon. The number of these pentameric repeats varies from 4 to 15 between strains and variation in repeat number results in the predicted SclB protein being either in or out of frame relative to the start codon. These observations suggest that expression of this protein may be regulated at the translational level as a result of gain or loss of CAAAA repeats. While the function of SclB remains to be elucidated, an sclB-specific transcript was detected by RT-PCR during in vitro culture. Finally, it is shown that a second gene, sclA, potentially encoding a protein with a similar extensive collagen-like structure and variable N-terminal sequence, is present in all isolates of S. pyogenes tested to date. Thus S. pyogenes harbours a novel family of structurally related and surface-exposed proteins of potential importance in the pathogenic process.

Amino Acid Sequence↗

Characterisation of the nitrile hydratase gene clusters of Rhodococcus erythropolis strains AJ270 and AJ300 and Microbacterium sp. AJ115 indicates horizontal gene transfer and reveals an insertion of IS1166.

The nitrile metabolising strains AJ270, AJ300 and AJ115 were isolated from the same location. The strains have very similar nitrile metabolising profiles. Sequencing of the 16S rRNA gene indicates that strains AJ270 and AJ300 are novel strains of Rhodococcus erythropolis while strain AJ115 is a novel Microbacterium strain very closely related to Microbacterium oxydans and Microbacterium liquefaciens. Analysis of the structure of the nitrile hydratase/amidase gene clusters in the three strains indicates that this region is identical in these strains and that this structure is different to other nitrile hydratase/amidase gene clusters. The major difference seen is the insertion of a complete copy of the insertion sequence IS1166 in the nhr2 gene. This copy of IS1166 generates a 10 bp direct duplication at the point of insertion and has one ORF encoding a protein of 434 amino acids, with 98% homology to the transposase of IS666 from Mycobacterium avium. A gene oxd, encoding aldoxime dehydratase is found upstream of the nitrile hydratase gene cluster and an open reading frame encoding a protein with homology to GlnQ type ABC transporters is found downstream of the nitrile hydratase/amidase genes. The identity of the nitrile hydratase/amidase gene clusters in the three strains suggests horizontal gene transfer of this region. Analysis of the strains for both linear and circular plasmids indicates that both are present in the strains but hybridisation studies indicate that the nitrile hydratase/amidase gene cluster is chromosomally located. The nitrile hydratase/amidase enzymes of strain AJ270 are inducible with acetonitrile or acetamide. Interestingly although a number of Fe-type nitrile hydratases have been shown to be photosensitive, the enzyme from strain AJ270 is not.

ATP-Binding Cassette Transporters↗

Transcriptional regulation in the Chlamydia trachomatis pCT plasmid.

We have analyzed transcriptional regulation of the chlamydial plasmid pCT. Transcription of a full-length 2.9-kb ORF1-ORF2 mRNA is likely to be regulated by the sigma 66 transcription factor which recognizes the TATAAT and TNGNCA sequences at the -10 and -35 DNA regions, respectively. RNA synthesis starts 39 nucleotides (nt) upstream from the ATG start codon of ORF1 and terminates within the downstream ORF3 DNA region. A 2.8-kb transcript transverses the ORF3-6 DNA region, while two transcripts of 2.2 and 1.9 kb cover the ORF4-6 DNA region. These mRNAs overlap two abundant transcripts which regulate the expression of the ORF3 and ORF4 genes. The accumulation of transcripts associated with these ORFs is likely to be regulated at the level of RNA synthesis by an unknown sigma factor which could select the RTTTAAA and TTYTTR sequences located at the -10 and -35 DNA regions, respectively. This new promoter consensus sequence could be unique to the gene expression machinery of Chlamydiae.

Bacterial Proteins↗

Equine infectious anemia virus gene expression: characterization of the RNA splicing pattern and the protein products encoded by open reading frames S1 and S2.

The utilization of predicted splice donor and acceptor sites in generating equine infectious anemia virus (EIAV) transcripts in fetal donkey dermal cells (FDD) was examined. A single splice donor site identified immediately upstream of the gag coding region joins the viral leader sequence to all downstream exons of spliced EIAV transcripts. The predominant 3.5-kb transcript synthesized in EIAV-infected FDD cells appears to be generated by a single splicing event which links the leader sequence to the first of two functional splice acceptor sites near the 5' end of the S1 open reading frame (ORF). The translation products encoded by the 3.5-kb transcript were examined by producing in vitro transcripts from a cDNA corresponding to this RNA followed by in vitro translation in wheat germ extracts. These transcripts directed the synthesis of three proteins: the virus trans-activator protein (EIAV Tat) encoded by ORF S1, a protein of unknown function encoded by ORF S2, and the virus envelope glycoprotein. When transfected into FDD cells, this cDNA also directed expression of EIAV Tat. Amino-terminal sequence analysis of the in vitro-synthesized S1 protein supports the suggestion that translation of EIAV Tat is initiated at a CUG codon within the virus leader region. Both in vitro-synthesized S2 protein and synthetic peptides corresponding to S2 are shown to react positively with sera obtained from EIAV-infected horses, providing the first direct evidence of expression of this protein in infected animals.

Amino Acid Sequence↗

Mucin biosynthesis: bovine C2GnT-M gene, tissue-specific expression, and herpes virus-4 homologue.

Mucin glycans are the major determinant of mucin functions. Mucin glycan branch structures, which increase structural heterogeneity and thus functional potential, are extended from beta6 N-acetylglucosaminides formed by beta6 N-acetylglucosaminyltransferases (beta6GnT). Core 2 beta6GnT-M (C2GnT-M) is the only branching enzyme that can synthesize all known mucin beta6 N-acetylglucosaminides. We report the cloning of four different bovine (b) C2GnT-M transcripts that are different only at 5'-untranslated regions. Two bC2GnT-M transcripts are found exclusively in tracheal epithelium and testis, whereas the other two are found in all other mucus-secreting tissues. The bC2GnT-M gene contains four exons spanning 5.3 kb, and the entire open reading frame is in one exon. The bC2GnT-M ORF has 95, 83, and 75% sequence identity to those of bovine herpes virus type 4 (BHV-4), human, and rat C2GnT-Ms, respectively. The homology between bovine and BHV-4 C2GnT-M genes is in the region between 170 nucleotides upstream from ATG start codon and 114 nucleotides downstream from TGA stop codon of the viral gene. Localized at the nonconserved region of the viral genome, the BHV-4 C2GnT-M gene is the only known viral C2GnT-M gene. The results suggest that BHV-4 acquired its C2GnT-M gene from the bovine gene. The mechanism of the viral acquisition of bC2GnT-M gene and the roles of the C2GnT-M gene in the survival and pathogenesis of this virus remain to be elucidated.

5' Untranslated Regions↗