Ujjwal Dasgupta

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The specificity of deletion formation was studied using tests involving reversion of palindromic insertion mutations. Insertions of a Tn5-related transposon at 13 sites in the ampicillin-resistance (amp) gene of plasmid pBR322 were shortened to a nested set of perfect palindromes, 22, 32 and 90 bp long. We monitored frequencies of reversion to Ampr, which(More)
It is now accepted that oral killed typhoid vaccines are not effective at inducing protective anti-typhoid immunity. It is not known whether oral killed Salmonella can function as an effective carrier of other antigens to the immune system. In order to test this hypothesis, we immunized groups of mice with viable and non-viable preparations of aroA(More)
A clinical isolate of Vibrio cholerae 01 was identified which did not possess the heat-labile (CT), the heat-stable (ST) or the zonula occludens (Zot) toxin genes. Rabbit ileal loop assays showed that no other CT-like toxin was produced by this strain. The partly deleted cholera toxin gene which carries the intact gene for the B subunit was cloned and the(More)
The IS50 elements, which are present as inverted repeats in the kanamycin-resistance transposon, Tn5, can move in unison carrying with them any interstitial DNA segment. In consequence, DNA molecules such as a lambda::Tn5 phage genome are composed of two overlapping transposons - the kan segment bracketed by IS50 elements (Tn5), and lambda bracketed by IS50(More)
Over a hundred years have elapsed since Vibrio cholerae, the etiological agent for the disease cholera, was discovered by Robert Koch. Ever since then serious efforts have been made to develop prophylactic measures to combat the disease without much success. Seven pandemics have so far been reported and cholera still remains a public health problem in(More)
Changes in the conformation of Complex III (CoQH2-cytochrome c reductase) of the mitochondrial respiratory chain were detected upon oxidoreduction using the nitroxide spin label, 3-(maleimidomethyl)-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl. EPR spectra of the spin label show a transition from a greater to a lesser degree of immobilization when the labeled(More)
We present a method for automatically detecting the number of sunspots and sunspot groups in standardized images of the Sun. We use adaptive thresholding to isolate the sunspots, and data clustering techniques to classify them into groups. By working on both the MDI Continuum and Magneto gram images, our method groups those sunspots together which originate(More)
Escherichia coli strain N100 has been mutagenized by transposon mutagenesis and mutants with a cell surface leaky phenotype have been isolated. The mutant designated as E. coli N100::Tn5 excreted periplasmic proteins like ribonuclease and alkaline phosphatase. When this mutant strain was transformed with plasmids containing cloned cholera toxin genes, the(More)
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