Restructuring α -pinene: novel entry into diverse polycarbocyclic frameworks

(-)-α-Pinene 1 has been restructured into a chiral cyclohexenone (+)-6, in which the functionalities were integrated to afford bicyclo[3.3.1]nonan 3,7-diones and a novel tricyclic skeleton 16 related to the sesquiterpene clovene. Intramolecular [2+2] photocycloadditions in (+)-6 and related 5-alkenylcyclohexenones provided an entry into some novel bridged tricyclic systems

Novel tandem ring-opening/ring-closing metathesis reactions of functionalized cyclohexenoids derived from (-)-α-pinene

The cyclohexenone (+)-2, readily obtained from (-)-α -pinene 1 was elaborated to (+)-3 in an attempt to construct the AB rings of taxoids employing the ring-closure metathesis (RCM) reaction as the key step. In the event, a novel ring-opening/ring-closing metathesis reaction was encountered in the relatively strain free cyclohexenyl ring of (+)-3

Reprogramming the tRNA-splicing activity of a bacterial RNA repair enzyme

Programmed RNA breakage is an emerging theme underlying cellular responses to stress, virus infection and defense against foreign species. In many cases, site-specific cleavage of the target RNA generates 2′,3′ cyclic phosphate and 5′-OH ends. For the damage to be repaired, both broken ends must be healed before they can be sealed by a ligase. Healing entails hydrolysis of the 2′,3′ cyclic phosphate to form a 3′-OH and phosphorylation of the 5′-OH to form a 5′-PO4. Here, we demonstrate that a polynucleotide kinase-phosphatase enzyme from Clostridium thermocellum (CthPnkp) can catalyze both of the end-healing steps of tRNA splicing in vitro. The route of tRNA repair by CthPnkp can be reprogrammed by a mutation in the 3′ end-healing domain (H189D) that yields a 2′-PO4 product instead of a 2′-OH. Whereas tRNA ends healed by wild-type CthPnkp are readily sealed by T4 RNA ligase 1, the H189D enzyme generates ends that are spliced by yeast tRNA ligase. Our findings suggest that RNA repair enzymes can evolve their specificities to suit a particular pathway

CTC1‐STN1 coordinates G‐ and C‐strand synthesis to regulate telomere length

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145241/1/acel12783.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145241/2/acel12783_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145241/3/acel12783-sup-0001-FigS1-S4.pd

DNA-induced dimerization of the single-stranded DNA binding telomeric protein Pot1 from Schizosaccharomyces pombe

Eukaryotic chromosome ends are protected from illicit DNA joining by protein–DNA complexes called telomeres. In most studied organisms, telomeric DNA is composed of multiple short G-rich repeats that end in a single-stranded tail that is protected by the protein POT1. Mammalian POT1 binds two telomeric repeats as a monomer in a sequence-specific manner, and discriminates against RNA of telomeric sequence. While addressing the RNA discrimination properties of SpPot1, the POT1 homolog in Schizosaccharomyces pombe, we found an unanticipated ssDNA-binding mode in which two SpPot1 molecules bind an oligonucleotide containing two telomeric repeats. DNA binding seems to be achieved via binding of the most N-terminal OB domain of each monomer to each telomeric repeat. The SpPot1 dimer may have evolved to accommodate the heterogeneous spacers that occur between S. pombe telomeric repeats, and it also has implications for telomere architecture. We further show that the S. pombe telomeric protein Tpz1, like its mammalian homolog TPP1, increases the affinity of Pot1 for telomeric single-stranded DNA and enhances the discrimination of Pot1 against RNA

Restructuring \alpha-pinene: novel entry into diverse polycarbocyclic frameworks

(-)-\alpha-Pinene 1 has been restructured into a chiral cyclohexenone (+)-6, in which the functionalities were integrated to afford bicyclo[3.3.1]nonan 3,7-diones and a novel tricyclic skeleton 16 related to the sesquiterpene clovene. Intramolecular [2+2]photocycloadditions in (+)-6 and related 5 alkenylcyclohexenones provided an entry into some novel bridged tricyclic systems

Novel tandem ring-opening/ring-closing metathesis reactions of functionalized cyclohexenoids derived from (−)-alpha-pinene

The cyclohexenone (+)-2, readily obtained from (−)-alpha-pinene 1 was elaborated to (+)-3 in an attempt to construct the AB rings of taxoids employing the ring-closure metathesis (RCM) reaction as the key step. In the event, a novel ring-opening/ring-closing metathesis reaction was encountered in the relatively strain free cyclohexenyl ring of (+)-3

The N Terminus of the OB Domain of Telomere Protein TPP1 Is Critical for Telomerase Action

Summary: Telomerase recruitment to telomeres and enzymatic processivity are mediated by TPP1, an essential component of telomere integrity and telomerase function. A surface on the OB domain of TPP1 called the TEL patch is critical for TPP1’s telomerase-associated functions. Here, we identify a separate region in the N terminus of the OB domain (termed NOB) of TPP1 that, like the TEL patch, is essential for telomerase repeat addition processivity in vitro as well as telomerase recruitment to telomeres and telomere lengthening in cells. Although well-conserved among most mammalian TPP1 homologs, the NOB region in mice is distinct. Swapping the sequence of human NOB into mouse TPP1 allows it to stimulate human telomerase, qualifying NOB as an important determinant of species specificity for TPP1-telomerase interaction. Our studies show that TPP1 NOB is critical for telomerase function and demonstrate that the telomerase interaction surface on TPP1 is more elaborate than previously appreciated. : TPP1 protein is critical for telomerase function and telomere length maintenance. Grill et al. find that the TPP1 NOB region is part of the surface that mediates these functions. The inability of mouse TPP1 to stimulate human telomerase is partially rescued by swapping in the human NOB sequence. Keywords: telomerase, telomeres, TPP1, TEL patch, telomerase processivity, telomerase recruitment, shelteri

The C-terminal domain of T4 RNA ligase 1 confers specificity for tRNA repair

T4 RNA ligase 1 (Rnl1) is a tRNA repair enzyme that thwarts a tRNA-damaging host response to virus infection. The 374-aa Rnl1 protein consists of an N-terminal nucleotidyltransferase domain fused to a unique C-terminal domain composed of 10 α helices. We exploited an in vitro tRNA splicing system to demonstrate that Rnl1 has an inherent specificity for sealing tRNA with a break in the anticodon loop. The tRNA specificity is imparted by the C domain, any deletion of which caused the broken tRNA to be sealed as poorly as the linear intron in vitro and also abolished Rnl1 tRNA splicing activity in vivo. Deletion analysis demarcated Rnl1-(1–254) as a minimal catalytic domain of Rnl1, capable of all chemical steps of the nonspecific RNA ligation reaction. Alanine scanning of the N domain identified Ser103, Leu104, Lys117, and Ser118 as important for pRNA ligation in vitro and tRNA repair in vivo