Single-stranded-DNA binding protein (SSB) levels during poststress recovery of Deinococcus radiodurans were significantly enhanced by 60 Co gamma rays or mitomycin C treatment but not by exposure to UV rays, hydrogen peroxide (H 2 O 2 ), or desiccation. Addition of rifampin prior to postirradiation recovery blocked such induction. In silico analysis of the ssb promoter region revealed a 17-bp palindromic radiation/desiccation response motif (RDRM1) at bp ؊114 to ؊98 and a somewhat similar sequence (RDRM2) at bp ؊213 to ؊197, upstream of the ssb open reading frame. Involvement of these cis elements in radiation-responsive ssb gene expression was assessed by constructing transcriptional fusions of edited versions of the ssb promoter region with a nonspecific acid phosphatase encoding reporter gene, phoN. Recombinant D. radiodurans strains carrying such constructs clearly revealed (i) transcriptional induction of the ssb promoter upon irradiation and mitomycin C treatment but not upon UV or H 2 O 2 treatment and (ii) involvement of both RDRM-like sequences in such activation of SSB expression, in an additive manner.Tolerance to high doses of ionizing radiation (X rays and gamma rays), which cause extensive and lethal DNA damage, is rare among life forms. However, species of the Gram-positive, pink-orange aerobic bacterium Deinococcus have been known to survive exposure to extremely high doses of ionizing radiation, UV rays, mitomycin C, desiccation, and other DNAdamaging agents (4, 30). Members of the family Deinococcaceae, comprising over 30 species, inhabit diverse environments and survive 5 kGy of 60 Co gamma rays without any loss of viability (31). Some of the strains are known to survive doses as high as even 15 kGy or more (13). The phenomena underlying such extremophilic behavior of deinococci, though not entirely clear, fall into three major categories. These are (i) a unique condensed organization of the genome, which minimizes DNA damage and facilitates rapid postirradiation repair (9,11,23,43); (ii) highly proficient, regular, and novel DNA repair mechanisms (6, 8) aided by proteins unique to deinococci (6, 38); and (iii) very capable enzymatic/nonenzymatic cleaning systems to scavenge reactive oxygen species (ROS) and protect proteins from oxidative damage (9, 10) or to degrade and resynthesize damaged proteins (22) in order to quickly alleviate the radiation toxicity and restore cellular homeostasis. Consequently, the conventional enzymes responsible for postirradiation recovery (PIR) survive and function with far better efficiency in deinococci (26). New mechanisms continue to be elaborated (20,22,42).Genomes of at least three highly radioresistant Deinococcus spp. have already been completely sequenced (14,26,39).These species are (i) D. radiodurans, the species of the first prototype strain isolated from irradiated meat cans 50 years ago and the most studied so far (1); (ii) the moderately thermophilic D. geothermalis, isolated from a hot spring in Italy (17); and (iii) the most recent, D. deserti,...

No abstract

The nitrogen-fixing cyanobacterium, Anabaena L-31 has two Hsp60 proteins, 59 kDa GroEL coded by the second gene of groESL operon and 61 kDa Cpn60 coded by cpn60 gene. Anabaena GroEL formed stable higher oligomer (>12-mer) in the presence of K(+) and prevented thermal aggregation of malate dehydrogenase (MDH). Using three protein substrates (MDH, All1541 and green fluorescent protein), it was found that the refolding activity of Anabaena GroEL was lower than that of Escherichia coli GroEL, but independent of both GroES and ATP. This correlated with in vivo data. GroEL exhibited ATPase activity which was enhanced in the presence of GroES and absence of a denatured protein, contrary to that observed for bacterial GroEL. However, a significant role for ATP could not be ascertained during in vitro folding assays. The monomeric Cpn60 exhibited much lower refolding activity than GroEL, unaffected by GroES and ATP. In vitro studies revealed inhibition of the refolding activity of Anabaena GroEL by Cpn60, which could be due to their different oligomeric status. The role of GroES and ATP may have been added during the course of evolution from the ancient cyanobacteria to modern day bacteria enhancing the refolding ability and ensuring wider scope of substrates for GroEL.

No abstract

Cellular temperature and pH govern many cellular physiologies, especially of cancer cells. Besides, attaining higher cellular temperature plays key role in therapeutic efficacy of hyperthermia treatment of cancer. This requires bio-compatible, non-toxic and sensitive probe with dual sensing ability to detect temperature and pH variations. In this regard, fluorescence based nano-sensors for cancer studies play an important role. Therefore, a facile green synthesis of orange carbon nano-dots (CND) with high quantum yield of 90% was achieved and its application as dual nano-sensor for imaging intracellular temperature and pH was explored. CND was synthesized from readily available, bio-compatible citric acid and rhodamine 6G hydrazide using solvent-free and simple heating technique requiring purification by dialysis. Although the particle size of 19 nm (which is quite large for CND) was observed yet CND exhibits no surface defects leading to decrease in photoluminescence (PL). On the contrary, very high fluorescence was observed along with good photo-stability. Temperature and pH dependent fluorescence studies show linearity in fluorescence intensity which was replicated in breast cancer cells. In addition, molecular nature of PL of CND was established using pH dependent fluorescence study. Together, the current investigation showed synthesis of highly fluorescent orange CND, which acts as a sensitive bio-imaging probe: an optical nano-thermal or nano-pH sensor for cancer-related studies.