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U DasGupta

Publications and source records attributed to U DasGupta.

6 recordsLinked to original sources
PubMed1998

Sequence comparison of the chromosomal regions encompassing the internalin C genes (inlC) of Listeria monocytogenes and L. ivanovii.

We have recently cloned and characterized the inlC gene of Listeria monocytogenes which belongs to the listerial internalin multigene family and codes for a 30-kDa secreted protein containing five consecutive leucine-rich repeats. Here, we show that in L. monocytogenes inlC is located between the rplS gene (encoding the 50S ribosomal protein L19), and the infC gene (encoding the translation initiation factor 3). By direct and inverse polymerase chain reactions (PCR), we cloned a 5.4-kb region containing a homologous gene (termed i-inlC) from L. ivanovii, the other pathogenic member of the genus Listeria. In this microorganism, the i-inlC gene is preceded by another internalin gene, i-inlD, which seems to be specific for L. ivanovii, as this gene could not be detected in L. monocytogenes by Southern hybridization with an i-inlD gene probe. The i-inlD gene also encodes a small secretory internalin (i-InlD), which shares extended homology with (i-)InlC. Upstream of i-inlD are genes for 23S rRNA and 5S rRNA, and two tRNA genes [Asn-tDNA (GTT) and Thr-tDNA(GTT)]. The 3' terminus of the Thr-tRNA gene appears to be the site of an insertion of a genetic element including i-inlC and i-inlD. A putative transcriptional regulator gene, the product of which contains the TetR family signature, is located downstream of i-inlC. This chromosomal position of the two inlC genes on their respective chromosomes may be due to horizontal transfer of this gene. Transcription of i-inlC and i-inlD is strictly dependent on the transcriptional activator PrfA, which regulates transcription of most of the known virulence genes (including inlC) of L. monocytogenes and of L. ivanovii.

Amino Acid Sequence↗
PubMed1987

Local DNA sequence control of deletion formation in Escherichia coli plasmid pBR322.

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 is the result of deletion of the palindrome plus one copy of the flanking 9 bp direct repeats (which had been formed by transposition). Revertant frequencies were found to depend on the location and the sequence of the palindromic insert. Changing a 45-kb interrupted palindrome to a 22-bp perfect palindrome stimulated deletion formation by factors of from fourfold to 545-fold among the 13 sites, while elongation of the perfect palindrome from 22 to 90 bp stimulated deletion formation by factors of from eight- to 18,000-fold. We conclude that deletion formation is strongly affected by subtle features of DNA sequence or conformation, both inside and outside the deleted segment, and that these effects may reflect specific interactions of DNA processing proteins with template DNAs.

Base Sequence↗
PubMed1985

IS50-mediated inverse transposition: specificity and precision.

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 elements. During direct transposition, mediated by IS50 "O" (outside) ends, the kan gene is moved and the lambda vector is left behind. During inverse transposition, mediated by the "I" (inside) ends of the IS50 elements, the lambda vector segment is moved and the kan gene is left behind. Direct transposition is several orders of magnitude more frequent than inverse transposition (Isberg and Syvanen, 1981; Sasakawa and Berg, 1982). We assessed the specificity and precision of the rare events mediated by pairs of I ends by mapping and sequencing independent inverse transpositions from a lambda::Tn5 phage into the amp and tet genes of plasmid pBR322. Using restriction analyses, 32 and 40 distinct sites of insertion were found among 46 and 72 independent inverse transpositions into the amp and tet genes, respectively. Eleven sites were used in two or more insertion events, and the two sites in tet used most frequently corresponded to major hotspots for the insertion of the Tn5 (by direct transposition). The sequences of 22 sites of inverse transposition (including each of the sites used more than once) were determined, in eleven cases by analyzing both pBR322-IS50 junctions, and in eleven others by sequencing one junction. The sequence of the "I" end of IS50 was preserved and 9-bp target sequence duplications were present in every case analyzed. GC pairs were found at each end of the target sequence duplication in ten of the eleven sites used more than once, and also in seven of the other eleven sites. Our data indicate that transposition mediated by pairs of "I" ends is similar in its specificity and precision to the more frequent transposition mediated by IS50 "O" ends.

Base Sequence↗
PubMed1979

Detection of conformational changes in complex III of the respiratory chain by a maleimido spin label.

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 enzyme, reduced either with ascorbate or sodium dithionite, is oxidized with potassium ferricyanide or ferricytochrome c. These observations are interpreted to indicate that Complex III is more compact in the reduced state at least in the locality of the spin label. An apparent increase in the concentration of total spins during oxidation of the complex suggests change in the interaction between the spin label and other paramagnetic centers and not an oxidation of spin label, itself, since reduced free spin label could not be reoxidized. Addition of antimycin A had no effect on the EPR spectrum of the spin-labeled enzyme, indicating that this inhibitor does not initiate a conformational change in the region of the spin label. Experiments in which N-ethyl-[2-3H] maleimide was bound to Complex III show that binding occurs primarily to a subunit with a molecular weight of 45,000. Although no qualitative differences were observed, it was found that less radioactivity appears in samples reduced with dithionite than in those reduced with ascorbate. This difference appears to be caused by decomposition products of dithionite.

Ascorbic Acid↗