The carbohydrate component of the enterobacterial common antigen (ECA) of Escherichia coli K-12 occurs primarily as a water-soluble cyclic polysaccharide located in the periplasm (ECA _CYC ) and as a phosphoglyceride-linked linear polysaccharide located on the cell surface (ECA _PG ). The polysaccharides of both forms are comprised of the amino sugars N -acetyl- d -glucosamine (GlcNAc), N -acetyl- d -mannosaminuronic acid (ManNAcA), and 4-acetamido-4,6-dideoxy- d -galactose (Fuc4NAc). These amino sugars are linked to one another to form trisaccharide repeat units with the structure →3-α- d -Fuc4NAc-(1→4)-β- d -ManNAcA-(1→4)-α- d -GlcNAc-(1→. The hydroxyl group in the 6 position of the GlcNAc residues of both ECA _CYC and ECA _PG are nonstoichiometrically esterified with acetyl groups. Random transposon insertion mutagenesis of E. coli K-12 resulted in the generation of a mutant defective in the incorporation of O -acetyl groups into both ECA _CYC and ECA _PG . This defect was found to be due to an insertion of the transposon into the yiaH locus, a putative gene of unknown function located at 80.26 min on the E. coli chromosomal map. Bioinformatic analyses of the predicted yiaH gene product indicate that it is an integral inner membrane protein that is a member of an acyltransferase family of enzymes found in a wide variety of organisms. The results of biochemical and genetic experiments presented here strongly support the conclusion that yiaH encodes the O -acetyltransferase responsible for the incorporation of O -acetyl groups into both ECA _CYC and ECA _PG . Accordingly, we propose that this gene be designated wecH .

The genetic variability of hepatitis B virus (HBV) represents a challenge for the sensitivity of immunologic and molecular based assays. Based on sequence divergences in the entire genome of >8 %, HBV genomes have been classified into ten genotypes designated as A to J. The aim of this study was to determine HBV genotypes and subtype in samples of HBV infected patients in Bangladesh. The sera samples were collected from chronically infected HBV patients. At first the DNA positive HBV samples were screened by EIA in our laboratory and the 1063 bp region of surface gene was amplified, sequenced and genotyped by sequence analysis. The same sequences were also used for subtypes and mutational analyses. After that, genotyping was also carried out by nested PCR using genotype specific primers in the same region of HBV surface gene. A total of 39 samples were sequencing to find out the genotypes and subtypes. It was found that the prevalent genotype was genotype C (subgenotype C1) which accounted for 48.7 %. The other genotypes found were genotype A (23.1 %) and genotype D (28.2 %). Predominant subtypes in Bangladesh were adr (41 %) followed by subtype adw2 (28.2 %), ayw3 (25.6 %), and others. Additionally, genotyping was also done by nested PCR using type-specific primers. In this method, out of 17 samples 6 were found to be genotype C, followed by genotype D (4 of 17) and genotype A (3 of 17). In PCR-based genotyping system we also observed the mix genotypes; 3 samples contained both genotype A and D, and 2 samples contained both C and D. The genetic diversity of HBV and distribution of its genotypes and subtypes amongst Bangladeshi population were done in this study, which will help us to provide information regarding circulating genotypes in this region and also help physicians to prescribe proper antiviral/interferon therapy.

The polysaccharide chains of enterobacterial common antigen (ECA) are comprised of the trisaccharide repeat unit Fuc4NAc-ManNAcA-GlcNAc, where Fuc4NAc is 4-acetamido-4,6-dideoxy -d- galactose, ManNAcA is N -acetyl -d- mannosaminuronic acid, and GlcNAc is N -acetyl -d- glucosamine. Individual trisaccharide repeat units are assembled as undecaprenyl-linked intermediates in a sequence of reactions that culminate in the transfer of Fuc4NAc from TDP-Fuc4NAc to ManNAcA-GlcNAc-pyrophosphorylundecaprenol (lipid II) to yield Fuc4NAc-ManNAcA-GlcNAc-pyrophosphorylundecaprenol (lipid III), the donor of trisaccharide repeat units for ECA polysaccharide chain elongation. Most of the genes known to be involved in ECA assembly are located in the wec gene cluster located at ca. 85.4 min on the Escherichia coli chromosome. The available data suggest that the structural gene for the TDP-Fuc4NAc:lipid II Fuc4NAc transferase also resides in the wec gene cluster; however, the location of this gene has not been unequivocally defined. Previous characterization of the nucleotide sequence of the wec gene cluster in the region between o416 and wecG revealed that it contained three open reading frames: o74 , o204 , and o450 . In contrast, the results of experiments described in the current investigation revealed that it contains only two open reading frames, o359 and o450 . Mutants of E. coli possessing null mutations in o359 were unable to synthesize ECA, and they accumulated lipid II. In addition, the in vitro incorporation of [ ³ H]FucNAc from TDP-[ ³ H]Fuc4NAc into lipid II was not observed in reaction mixtures using cell extracts obtained from these mutants as a source of enzyme. The ECA-negative phenotype of these mutants was complemented by plasmid constructs containing the wild-type o359 allele, and Fuc4NAc transferase activity was demonstrated by using cell extracts obtained from the complemented mutants. Furthermore, partially purified o359 gene product, expressed as recombinant C-terminal His-tagged protein, was able to catalyze the in vitro transfer of [ ³ H]Fuc4NAc from TDP-[ ³ H]Fuc4NAc to lipid II. Our data support the conclusion that o359 of the wec gene cluster of E. coli is the structural gene for the TDP-Fuc4NAc:lipid II Fuc4NAc transferase involved in the synthesis ECA trisaccharide repeat units.

Cloning and DNA sequencing of gamma-hemolysin genes from two strains of Staphylococcus aureus showed three open reading frames, transcribed serially within the sequenced 4353 nucleotide bases. In this report, from the nucleotide sequence, we demonstrate that leukocidin and gamma-hemolysin share the F or H gamma I component and the specificity of both toxins depends on this component.

The development of safe and effective vaccines has been an overriding priority for controlling the 2019-coronavirus disease (COVID-19) pandemic. From the onset, COVID-19 has caused high mortality and economic losses and yet has also offered an opportunity to advance novel therapeutics such as DNA and mRNA vaccines. Although it is hoped that the swift acceptance of such vaccines will prevent loss of life, rejuvenate economies and restore normal life, there could also be significant pitfalls. This perspective provides an overview of future directions and challenges in advancing promising vaccine platforms to widespread therapeutic use.