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Biomedical subjects

N Banerjee

Publications and source records attributed to N Banerjee.

At least 19 recordsLinked to original sources
PubMed1996

The Ustilago maydis virally encoded KP1 killer toxin.

Some strains of the plant-pathogenic fungus Ustilago maydis secrete toxins (killer toxins) that are lethal to susceptible strains of the same fungus. There are three well-characterized killer toxins in U. maydis-KP1, KP4, and KP6-which are secreted by the P1, P4, and P6 subtypes, respectively. These killer toxins are small polypeptides encoded by segments of an endogenous, persistent double-stranded RNA (dsRNA) virus in each U. maydis subtype. In P4 and P6, the M2 dsRNA segment encodes the toxin. In this work, the KP1 killer toxin was purified for internal amino acid sequence analysis, and P1M2 was identified as the KP1 toxin-encoding segment by sequence analysis of cDNA clones. The KP1 toxin is a monomer with a predicted molecular weight of 13.4kDa and does not have extensive sequence similarity with other viral anti-fungal toxins. The P1M2 segment is different from the P4 and P6 toxin-encoding dsRNA segments in that the 3' non-coding region of its plus strand has no sequence homology to the 3' ends of the plus strands of P1M1, P4M2, or P6M2.

Cloning, Molecular↗
PubMed1995

A single nucleotide change in the coat protein gene of tobacco mosaic virus is involved in the induction of severe chlorosis.

YSI/1 is a mutant of the common strain (U1) of tobacco mosaic virus (TMV) which induces a severe yellow mosaic in Nicotiana tabacum instead of the light green/dark green mosaic induced by its parental U1 virus. Although there was less coat protein (CP) in whole leaf extracts of YSI/1-infected leaves than in U1-infected leaves, severalfold more CP was found in the chloroplasts, most of which was associated with the thylakoids. Sequencing the CP genes of both viruses showed the presence of nucleotide differences at viral RNA positions 5770 and 6127, both of which result in amino acid replacements; YSI/1 has an Asp-->Val change at amino acid 19 and a Ser-->Phe change at amino acid 138. A common strain TMV engineered to contain the YSI/1 3' end sequences, including the CP, induced the severe yellow mosaic of the YSI/1 mutant. A chimeric virus with the change only at nucleotide 5770 (amino acid 19) in the CP induced a severe yellow mosaic, showing that this replacement is involved in the induction of chlorosis by YSI/1. A second isolate of the same chimera also induced severe yellow mosaic symptoms; sequencing showed that it had gained the change at nucleotide 6127. However, a chimeric virus with the change only at nucleotide 6127 (amino acid 138) in the CP was unable to induce the severe yellow mosaic.

Base Sequence↗
PubMed1995

Expression and characterization of the ponA (ORF I) gene of Haemophilus influenzae: functional complementation in a heterologous system.

The coding sequence of the Haemophilus influenzae ORF I gene was amplified by PCR and cloned into different Escherichia coli expression vectors. The ORF I-encoded protein was approximately 90 kDa and bound 3H-benzyl-penicillin and 125I-cephradine. This high-molecular-weight penicillin-binding protein (PBP) was also shown to possess transglycosylase activity, indicating that the ORF I product is a bifunctional PBP. The ORF I protein was capable of maintaining the viability of E. coli delta ponA ponB::spcr cells in transcomplementation experiments, establishing the functional relevance of the significant amino acid homology seen between E. coli PBP 1A and 1B and the H. influenzae ORF I product. In addition, the physiological functioning of the H. influenzae ORF I (PBP 1A) product in a heterologous species established the ability of the enzyme not only to recognize the E. coli substrate but also to interact with heterologous cell division proteins. The affinity of the ORF I product for 3H-benzylpenicillin and 125I-cephradine, the MIC of beta-lactams for E. coli delta ponA ponB::spcr expressing the ORF I gene, and the amino acid alignment of the PBP 1 family of high-molecular-weight PBPs group the ORF I protein into the PBP 1A family of high-molecular-weight PBPs.

Bacterial Proteins↗
PubMed1992

Leishmania donovani: isolation of a concanavalin-A specific antigen and its evaluation for serodiagnosis of visceral leishmaniasis.

A glycoconjugate antigen of 27-39 kDa was isolated from a cell-free extract of Leishmania donovani by affinity chromatography using a Concanavalin-A sepharose-4B column and eluted with 0.5 M alpha-methylmannoside. The antigen was recognized specifically by sera from kala-azar (visceral leishmaniasis) patients and did not react with sera from tuberculosis, leprosy or malaria patients. The antigen may therefore be useful in developing a serodiagnostic assay for visceral leishmaniasis.

Animals↗
PubMed1990

Lipid A mutants of Vibrio cholerae: isolation and partial characterization.

Vibrio cholerae mutants resistant to common antibiotics and neutral and anionic detergents were isolated. Analysis of isolated outer membranes revealed a significant deficiency in the acylation of lipid A in the resistant strains. The content of amide-linked and ester-bound fatty acids in the lipid A of the mutant strains compared to that of the wild type was about 50-56% and 29-37% respectively. This defect was specific for lipid A as there was no change in the acylation of phospholipids. The reduction in fatty acid content of lipid A was reflected in the altered endotoxic properties in the mutant strains.

Drug Resistance, Microbial↗
PubMed1990

Ustilago maydis KP6 killer toxin: structure, expression in Saccharomyces cerevisiae, and relationship to other cellular toxins.

There are a number of yeasts that secrete killer toxins, i.e., proteins lethal to sensitive cells of the same or related species. Ustilago maydis, a fungal pathogen of maize, also secretes killer toxins. The best characterized of the U. maydis killer toxins is the KP6 toxin, which consists of two small polypeptides that are not covalently linked. In this work, we show that both are encoded by one segment of the genome of a double-stranded RNA virus. They are synthesized as a preprotoxin that is processed in a manner very similar to that of the Saccharomyces cerevisiae k1 killer toxin, also encoded by a double-strand RNA virus. Active U. maydis KP6 toxin was secreted from S. cerevisiae transformants expressing the KP6 preprotoxin. The two secreted polypeptides were not glycosylated in U. maydis, but one was glycosylated in S. cerevisiae. Comparison of known and predicted cleavage sites among the five killer toxins of known sequence established a three-amino-acid specificity for a KEX2-like enzyme and predicted a new, undescribed processing enzyme in the secretory pathway in the fungi. The mature KP6 toxin polypeptides had hydrophobicity profiles similar to those of other known cellular toxins.

Amino Acid Sequence↗
PubMed1989

A very small viral double-stranded RNA.

UmV is a double-stranded RNA (dsRNA) virus of the corn fungal pathogen Ustilago maydis. UmV has no infectious cycle. Some UmV subtypes have viral dsRNAs encoding secreted toxins that kill sensitive cells of the same species and related species. There are three viral subtypes, P1, P4 and P6, which differ in the specificity of their secreted killer toxins. Each has three size classes of dsRNA: H (heavy), M (medium) and L (light). The L segments of UmV are unique in being derived from one end of the larger M segments. We have sequenced P1 L and placed it at the 3' end of the P1 M1 plus strand. In their overlapping regions, these dsRNAs are identical in sequence. In vitro translation of P1 M1 results in a peptide whose size is consistent with its being encoded by the non-L region of M1. P1 L is a very small dsRNA of 355 bp. It has no long open reading frames and produces no detectable in vitro translation product. The sequence of P1 L suggests that it is derived by a process unique among dsRNA viruses: replication and packaging of the 3' end fragment of a processed mRNA.

Base Sequence↗
PubMed1986

Elongation of C20 polyunsaturated fatty acids by human skin fibroblasts.

Human skin fibroblasts actively elongate a portion of incorporated C20 polyunsaturated fatty acids to their respective C22 derivatives. As much as 40% of incorporated [14C]eicosapentaenoate is elongated within 8 h and 85% by 48 h. Elongation of [14C]arachidonate is initially less than half that of [14C]eicosapentaenoate and plateaus at 20-30% of incorporated 14C-labeled fatty acid. The elongation of 5,8,11-[14C]eicosatrienoate is intermediate between that of 20:4(n-6) and 20:5(n-3). Docosatetraenoate is not an effective inhibitor of the elongation of arachidonate, thus suggesting that the observed plateau is not due to product inhibition. When concentrations of exogenous fatty acids are increased, these cells elongate substantial quantities of C20 polyunsaturated fatty acids; elongation of eicosapentaenoate is consistently more extensive than that of arachidonate. Eicosapentaenoate is also an effective inhibitor of the elongation of [14C]arachidonate. Increases in exogenous arachidonate up to 10 microM result in an increase in elongation of [14C]arachidonate both in absolute quantities and as a percentage of that incorporated; the arachidonate thus acts as a positive modulator of its own elongation. Increased eicosapentaenoate also enhances the elongation of [14C]eicosapentaenoate, but only at lower concentrations (0.02-0.15 microM). The factors which regulate the elongation of C20 polyunsaturated fatty acids in human skin fibroblasts serve to permit extensive elongation of eicosapentaenoate while retaining incorporated arachidonate primarily in its C20 form.

8,11,14-Eicosatrienoic Acid↗
PubMed1985

High-affinity incorporation of 20-carbon polyunsaturated fatty acids by human skin fibroblasts.

This study has examined the acyl specificity of incorporation of polyunsaturated fatty acids into cellular glycerolipids of human skin fibroblasts. At low exogenous fatty acid concentrations (0.2-1.2 microM) the extent of incorporation of arachidonate, eicosapentaenoate, 8,11,14-eicosatrienoate and 5,8,11-eicosatrienoate is 60-150% greater than that of oleate or linoleate. As the concentration of exogenous free fatty acid is increased to 25 microM, there is little decrease in the percentage of exogenous oleate incorporated into cellular glycerolipids. Under these conditions, the percentage incorporation of arachidonate and eicosapentaenoate drops 2-3-fold and approaches that of oleate. In contrast, the percentage incorporation of 8,11,14-eicosatrienoate remains high as exogenous fatty acid concentrations are increased. Incorporation of arachidonate, eicosapentaenoate, 8,11,14-eicosatrienoate and 5,8,11-eicosatrienoate is inhibited by addition of any of the other C20 polyunsaturated fatty acids but not by palmitate or oleate. C20 polyunsaturated fatty acids other than the eicosanoid precursors are also not effective inhibitors of arachidonate incorporation. The high affinity incorporation of C20 polyunsaturated fatty acids does not appear to be due to their selective esterification in any one class of cellular phospholipids. These results are compatible with a model of two pathways of fatty acids incorporation into mammalian cells. One pathway utilizes all exogenous long-chain fatty acids and, at least in fibroblasts, is not readily saturable. The second is a high-affinity, low-capacity uptake mechanism specific for arachidonate and other precursors of eicosanoids. The acyl specificity of this latter pathway appears to be similar to that of platelet arachidonyl- CoA synthetase. Results obtained with 8,11,14-eicosatrienoate would indicate, however, that at high concentrations, additional mechanisms influence the acyl specificity of fatty acid incorporation in these cells.

8,11,14-Eicosatrienoic Acid↗
PubMed1984

Gene heterogeneity: a basis for alternative 5.8S rRNA processing.

Two bands of 5.8S rRNA were observed when the total RNA isolated from rat or mouse tissue was separated by electrophoresis on high-resolution polyacrylamide gels under denaturing conditions. The minor form, with a lower mobility, represented 15-35% of the total 5.8S rRNA, depending on the source of the tissue. Sequence analysis and the kinetics of formation showed that this minor form is elongated at the 5' end and is not a precursor. The sequence of the minor form was found to be p(C)CGAUA[CG-, five or six nucleotides longer than the major form. The minor 5.8S rRNA constituent also formed a more stable junction complex with 28S rRNA than the shorter major sequence. The rat DNA sequence that corresponds to the additional nucleotides at the 5' end of 5.8S rRNA has been reported to be -CCGTACG-[Subrahmanyam, C. S., Cassidy, B., Busch, H., & Rothblum, L. I. (1982) Nucleic Acids Res. 10, 3667-3680], a sequence which does not contain the extra adenylic acid residue at position 4 found in the minor form. This suggests that the rodent rRNA genes are heterogeneous and that the insertion of an A residue in the ribosomal precursor RNA can generate an alternate processing site.

Animals↗
PubMed1981

Effect of point mutations on 5.8S ribosomal ribonucleic acid secondary structure and the 5.8S--28S ribosomal ribonucleic acid junction.

Naturally occurring differences in the nucleotide sequences of 5.8S ribosomal ribonucleic acids (rRNAs) from a variety of organisms have been used to study the role of specific nucleotides in the secondary structure and intermolecular interactions of this RNA. Significant differences in the electrophoretic mobilities of free 5.8S RNAs and the thermal stabilities of 5.8S--28S rRNA complexes were observed even in such closely related sequences as those of man, rat, turtle, and chicken. A single base transition from a guanylic acid residue in position 2 in mammalian 5.8S rRNA to an adenylic acid residue in turtle and chicken 5.8S rRNA results both in a more open molecular conformation and in a 5.8S--28S rRNA junction which is 3.5 degrees C more stable to thermal denaturation. Other changes such as the deletion of single nucleotides from either the 5' or the 3' terminals have no detectable effect on these features. The results support secondary structure models for free 5.8S rRNA in which the termini interact to various degrees and 5.8S--28S rRNA junctions in which both termini of the 5.8S molecule interact with the cognate high molecular weight RNA component.

Alkaline Phosphatase↗