http://192.168.1.40:8080/xmlui/handle/123456789/1148 Sun, 31 May 2026 13:43:15 GMT 2026-05-31T13:43:15Z http://192.168.1.40:80/xmlui/bitstream/id/864b50d3-e3f1-4a57-82de-49161f578785/sujoy.jpg http://192.168.1.40:8080/xmlui/handle/123456789/1148 http://192.168.1.40:8080/xmlui/handle/123456789/2174 The dimeric repressor SoxR binds cooperatively to the promoter(s) regulating expression of the sulfur oxidation (sox) operon of Pseudaminobacter salicylatoxidans KCT001 Mandal, Sukhendu; Chatterjee, Sujoy; Dam, Bomba; Roy, Pradosh; Das Gupta, Sujoy K. Sulfur oxidation in Pseudaminobacter salicylatoxidans KCT001 is rendered by the combined action of several enzymes encoded by a thiosulfate-inducible sox operon. In this study it has been conclusively demonstrated by insertional mutagenesis that the regulatory gene of this operon is soxR, which encodes a DNA-binding protein belonging to the ArsR-SmtB family. SoxR was found to bind to two promoter-operator segments within the sox cluster, of which the one (wx) located between soxW and soxX controls the expression of sulfur-oxidation genes soxX through soxD while the other, a bi-directional element (sv) located between soxS and soxV, controls the expression of soxVW in one direction and the putative regulatory cluster soxSRT in the other. In the case of the wx promoter the repressor was found to bind in a cooperative manner to two distinct binding sites having different affinities, while in the case of the sv promoter binding occurred at a symmetric dimeric site and involved a higher degree of cooperativity. The high degree of cooperativity observed in the binding of SoxR to its target sites seemed to be due to the propensity of SoxR monomers to form dimers. The apparent dissociation constants of the SoxR-operator complexes were in the nanomolar range, indicating relatively strong interactions. It was demonstrated using a reporter system in Escherichia coli that this high-affinity binding of SoxR led to efficient repression in trans. Thus the role of SoxR as a repressor of the sox operon has not only been conclusively established but it has also been shown that this repression is brought about through cooperative interactions of SoxR with dimeric binding sites that occlude the operon promoters. DOI: 10.1099/mic.0.29197-0 Mon, 01 Jan 2007 00:00:00 GMT http://192.168.1.40:8080/xmlui/handle/123456789/2174 2007-01-01T00:00:00Z http://192.168.1.40:8080/xmlui/handle/123456789/2115 Cloning, characterization and expression analysis of nucleotide metabolism-related genes of mycobacteriophage L5 Bhattacharya, B.; Giri, N.; Mitra, M.; Dasgupta, Sujoy Kumar The genomes of mycobacteriophages of the L5 family, which includes the lytic phage D29, contain several genes putatively linked to nucleotide- metabolizing functions. Two such genes, 48 and 50, encoding thymidylate synthase and ribonucleotide reductase (RNR), respectively, were overexpressed in Escherichia coli and the recombinant proteins were biochemically characterized. It was established that Gp50 was a class II RNR having properties similar to that of the corresponding enzyme from Lactobacillus leichmanni, whereas Gp48 was a flavin-dependent thymidylate synthase (ThyX) that resembled the Paramecium bursaria chlorella virus-1 ThyX enzyme in its properties. That both these proteins play a role in phage development was evident from the observation that they were detectable soon after the lytic phase of growth commenced. Gp48 and 50 were also found to coimmunoprecipitate, which indicates the possible existence of an L5 thymidylate synthase complex. Thymidylate synthase assays revealed that during the intracellular stage of phage growth, a significant decrease in the host thymidylate synthase (ThyA) activity occurred. It appears that synthesis of the viral enzyme (ThyX) is necessary to compensate for this loss in activity. In general, the results suggest that phage-encoded nucleotide metabolism-related functions play an important role in the lytic propagation of L5 and related mycobacteriophages DOI: 10.1111/j.1574-6968.2007.01047.x Sat, 01 Mar 2008 00:00:00 GMT http://192.168.1.40:8080/xmlui/handle/123456789/2115 2008-03-01T00:00:00Z http://192.168.1.40:8080/xmlui/handle/123456789/2113 Modulation of DNA-binding activity of Mycobacterium tuberculosis HspR by chaperones Das Gupta, Twishasri; Bandyopadhyay, Boudhayan; Dasgupta, Sujoy Kumar In Mycobacterium tuberculosis, hspR is the last gene of the dnaKJE operon. It encodes the repressor HspR, which regulates the expression from this operon by binding to a consensus upstream sequence known as HAIR (HspR-associated inverted repeats). Previous investigations in the related Gram-positive bacterium Streptomyces coelicolor have revealed that DnaK acts as a co-repressor for HspR. In this investigation, a similar situation was encountered using the corresponding mycobacterial pair. However, the novel feature unearthed in this study is that the mycobacterial GroELs, GroEL1 and GroEL2, considerably stimulate the HAIR-binding activity of the HspR-DnaK combination. That these GroELs play a role in the folding process was evident from the observation that when heat- or chemically denatured HspR was renatured, the protein gained optimal activity only if one of these GroEL class chaperones was present along with DnaK. The renaturation process was found to be dependent on ATP hydrolysis. The DnaK-dependent DNA-binding activity of HspR could also be stimulated by DnaJ, but GrpE, which is known to release DnaK-bound substrates, was found to be inhibitory. The results of this study suggest that protein folding plays a substantial role in the activation of HspR following heat shock and that DnaK may be involved in two ways - first, as a chaperone acting in concert with GroEL and/or DnaJ and second, as a co-repressor bound to HspR. DOI: 10.1099/mic.0.2007/012294-0 Fri, 01 Feb 2008 00:00:00 GMT http://192.168.1.40:8080/xmlui/handle/123456789/2113 2008-02-01T00:00:00Z http://192.168.1.40:8080/xmlui/handle/123456789/2110 DNA bending in the mycobacterial plasmid pAL5000 origin-RepB complex Chatterjee, Sujoy; Basu, Arnab; Basu, Abhijit; Dasgupta, Sujoy Kumar Plasmid pAL5000 represents a family of relatively newly discovered cryptic plasmids in gram-positive Actinomycetes bacteria. The replication regions of these plasmids comprise a bicistronic operon, repA-repB, encoding two replication proteins. Located upstream is a cis-acting element that functions as the origin of replication. It comprises an similar to 200-bp segment spanning two binding sites for the replication protein RepB, a low-affinity (L) site and a high-affinity (H) site separated by an similar to 40-bp spacer sequence. The trajectory of the DNA in the RepB-origin complex has been investigated, and it has been found that the origin undergoes significant bending movements upon RepB binding. RepB binding not only led to local bending effects but also caused a long-range polar curvature which affected the DNA sequences 3' to the H site. These movements appear to be essential for the in-phase alignment of the L and H sites that leads to the formation of a looped structure. A novel property of RepB unearthed in this study is its ability to form multimers. This property may be an important factor that determines the overall trajectory of the DNA in the RepB-origin complex. The results presented in this study suggest that the origins of replication of pAL5000 and related plasmids are highly flexible and that multimeric, RepB-like initiator proteins bind the origin and induce local deformations and long-range curvatures which are probably necessary for the proper functioning of the origin. DOI: 10.1128/JB.01155-07 Sat, 01 Dec 2007 00:00:00 GMT http://192.168.1.40:8080/xmlui/handle/123456789/2110 2007-12-01T00:00:00Z