Structural basis for CRISPR RNA-guided DNA recognition by Cascade

The CRISPR (clustered regularly interspaced short palindromic repeats) immune system in prokaryotes uses small guide RNAs to neutralize invading viruses and plasmids. In Escherichia coli, immunity depends on a ribonucleoprotein complex called Cascade. Here we present the composition and low-resolution structure of Cascade and show how it recognizes double-stranded DNA (dsDNA) targets in a sequence-specific manner. Cascade is a 405-kDa complex comprising five functionally essential CRISPR-associated (Cas) proteins (CasA1B2C6D1E1) and a 61-nucleotide CRISPR RNA (crRNA) with 5′-hydroxyl and 2′,3′-cyclic phosphate termini. The crRNA guides Cascade to dsDNA target sequences by forming base pairs with the complementary DNA strand while displacing the noncomplementary strand to form an R-loop. Cascade recognizes target DNA without consuming ATP, which suggests that continuous invader DNA surveillance takes place without energy investment. The structure of Cascade shows an unusual seahorse shape that undergoes conformational changes when it binds target DNA.

Dipoid-Specific Genome Stability Genes of S. cerevisiae: Genomic Screen Reveals Haploidization as an Escape from Persisting DNA Rearrangement Stress

Maintaining a stable genome is one of the most important tasks of every living cell and the mechanisms ensuring it are similar in all of them. The events leading to changes in DNA sequence (mutations) in diploid cells occur one to two orders of magnitude more frequently than in haploid cells. The majority of those events lead to loss of heterozygosity at the mutagenesis marker, thus diploid-specific genome stability mechanisms can be anticipated. In a new global screen for spontaneous loss of function at heterozygous forward mutagenesis marker locus, employing three different mutagenesis markers, we selected genes whose deletion causes genetic instability in diploid Saccharomyces cerevisiae cells. We have found numerous genes connected with DNA replication and repair, remodeling of chromatin, cell cycle control, stress response, and in particular the structural maintenance of chromosome complexes. We have also identified 59 uncharacterized or dubious ORFs, which show the genome instability phenotype when deleted. For one of the strongest mutators revealed in our screen, ctf18Δ/ctf18Δ the genome instability manifests as a tendency to lose the whole set of chromosomes. We postulate that this phenomenon might diminish the devastating effects of DNA rearrangements, thereby increasing the cell's chances of surviving stressful conditions. We believe that numerous new genes implicated in genome maintenance, together with newly discovered phenomenon of ploidy reduction, will help revealing novel molecular processes involved in the genome stability of diploid cells. They also provide the clues in the quest for new therapeutic targets to cure human genome instability-related diseases

EVALUATION OF ANTHELMINTIC ACTIVITY OF INDIGENOUS HERBAL FORMULATION IN GOATS

A study was undertaken to evaluate the efficacy of indigenous herbal formualtion comprising of bark of A. indica, seeds of Nigella sativa and Butea frondosa and fruits of Piper longum against clinical helmintic infection in goats at dose levels 5 and 10 gm/day/ animal once a day and twice a day. Administration of the herbal formulation twice a day significantly reduced the worm infection and found to be more effective as compared to administration of the doses once a day

Thermodynamically stable octahedral MoS<inf>2</inf> in van der Waals hetero-bilayers

Reversible switching of the structural ground state of a solid is a fundamental goal in materials engineering, which has not been achieved in atomically thin layers of van der Waals crystals. This is particularly important for the transition metal dichalcogenides, such as molybdenum disulphide (MoS2), where the higher-energy octahedral polymorphs exhibit a wide range of fascinating properties. Here we show that thermodynamically stable octahedral phase of monolayer MoS2 can be achieved in coexistence with the 1H phase, at temperatures below ∼500 K, by forming a van der Waals hybrid with another layered solid, such as hexagonal boron nitride (hBN) or graphene. Spatial mapping and temperature-dependence of the zone-folded Raman modes reveal that the octahedral phase exists only within the heterostructure region, and exhibits remarkable stability to repeated thermal cycling. A concurrent shift in the out-of-plane A 1g vibrational mode of MoS2, and near-absence of the octahedral phase in homo-epitaxial structures, suggest likely role of local lattice relaxation due to incommensurability-driven stress fields. Our experiment establishes van der Waals hetero-epitaxy as a new tool for crystal structure engineering in atomic membranes