Type II restriction-modification (R-M) systems comprise a restriction endonuclease (REase) and a protective methyltransferase (MTase). After R-M genes enter a new cell, MTase must appear before REase or the chromosome will be cleaved. PvuII and some other R-M systems achieve this delay by cotranscribing the REase gene with the gene for an autogenous transcription activator (the controlling or ‘C’ protein C.PvuII). This study reveals, through in vivo titration, that C.PvuII is not only an activator but also a repressor for its own gene. In other systems, this type of circuit can result in oscillatory behavior. Despite the use of identical, symmetrical C protein-binding sequences (C-boxes) in the left and right operators, C.PvuII showed higher in vitro affinity for OL than for OR, implicating the spacer sequences in this difference. Mutational analysis associated the repression with OR, which overlaps the promoter −35 hexamer but is otherwise dispensable for activation. A nonrepressing mutant exhibited poor establishment in new cells. Comparing promoter-operator regions from PvuII and 29 R-M systems controlled by C proteins revealed that the most-highly conserved sequence is the tetranucleotide spacer separating OL from OR. Any changes in that spacer reduced the stability of C.PvuII-operator complexes and abolished activation.

Capacitation is an important physiological pre-requisite before the sperm cell can acrosome react and fertilize the oocyte. Recent reports from several laboratories have amply documented that the protein phosphorylation especially at tyrosine residues is one of the most important events that occur during capacitation. In this article, we have reviewed the data from our and other laboratories, and have constructed a heuristic model for the mechanisms and molecules involved in capacitation/acrosome reaction.

Coconut, cocoa and arecanut are commercial plantation crops that play a vital role in the Indian economy while sustaining the livelihood of more than 10 million Indians. According to 2012 Food and Agricultural organization's report, India is the third largest producer of coconut and it dominates the production of arecanut worldwide. In this study, three Plant Growth Promoting Rhizobacteria (PGPR) from coconut (CPCRI-1), cocoa (CPCRI-2) and arecanut (CPCRI-3) characterized for the PGP activities have been sequenced. The draft genome sizes were 4.7 Mb (56% GC), 5.9 Mb (63.6% GC) and 5.1 Mb (54.8% GB) for CPCRI-1, CPCRI-2, CPCRI-3, respectively. These genomes encoded 4056 (CPCRI-1), 4637 (CPCRI-2) and 4286 (CPCRI-3) protein-coding genes. Phylogenetic analysis revealed that both CPCRI-1 and CPCRI-3 belonged to Enterobacteriaceae family, while, CPCRI-2 was a Pseudomonadaceae family member. Functional annotation of the genes predicted that all three bacteria encoded genes needed for mineral phosphate solubilization, siderophores, acetoin, butanediol, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, chitinase, phenazine, 4-hydroxybenzoate, trehalose and quorum sensing molecules supportive of the plant growth promoting traits observed in the course of their isolation and characterization. Additionally, in all the three CPCRI PGPRs, we identified genes involved in synthesis of hydrogen sulfide (H2S), which recently has been proposed to aid plant growth. The PGPRs also carried genes for central carbohydrate metabolism indicating that the bacteria can efficiently utilize the root exudates and other organic materials as energy source. Genes for production of peroxidases, catalases and superoxide dismutases that confer resistance to oxidative stresses in plants were identified. Besides these, genes for heat shock tolerance, cold shock tolerance and glycine-betaine production that enable bacteria to survive abiotic stress were also identified.

S N 1-type methylating agents generate O 6 -methyl guanine (O 6 -meG), which is a potently mutagenic, toxic, and recombinogenic DNA adduct. Recognition of O 6 -meG:T mismatches by mismatch repair (MMR) causes sister chromatid exchanges, which are representative of homologous recombination (HR) events. Although the MMR dependent mutagenicity and toxicity caused by O 6 -meG has been studied, the mechanisms of recombination induced by O 6 -meG are poorly understood. To explore the HR and MMR genetic interactions in mammals, we used the Rad51d and Mlh1 mouse models. Ablation of Mlh1 did not appreciably influence the developmental phenotypes conferred by the absence of Rad51d. Mouse embryonic fibroblasts (MEFs) deficient in Rad51d can only proliferate in p53-deficient background. Therefore, Rad51d −/− Mlh1 −/− Trp53 −/− MEFs with a combined deficiency of HR and MMR were generated and comparisons between MLH1 and RAD51D status were made. To our knowledge, these MEFs are the first mammalian model system for combined HR and MMR defects. Rad51d-deficient MEFs were 5.3 fold sensitive to N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) compared to the Rad51d-proficient MEFs. A pronounced G2/M arrest in Rad51d-deficient cells was accompanied by an accumulation of γ-H2AX and apoptosis. Mlh1-deficient MEFs were resistant to MNNG and showed no G2/M arrest or apoptosis at the doses used. Importantly, loss of Mlh1 alleviated sensitivity of Rad51d-deficient cells to MNNG, in addition to reducing γ-H2AX, G2/M arrest and apoptosis. Collectively, the data support the hypothesis that MMR-dependent sensitization of HRdeficient cells is specific for O 6 -meG and suggest that HR resolves DNA intermediates created by MMR recognition of O 6 -meG:T. This study provides insight into recombinogenic mechanisms of carcinogenesis and chemotherapy resulting from O 6 -meG adducts.