A highly conserved repetitive DNA sequence, (TTAGGG)., has been isolated from a human recombinant repetitive DNA library. Quantitative hybridization to chromosomes sorted by flow cytometry indicates that comparable amounts of this sequence are present on each human chromosome. Both fluorescent in situ hybridization and BAL-31 nuclease digestion experiments reveal major clusters of this sequence at the telomeres of all human chromosomes. The evolutionary conservation of this DNA sequence, its terminal chromosomal location in a variety of higher eukaryotes (regardless of chromosome number or chromosome length), and its similarity to functional telomeres isolated from lower eukaryotes suggest that this sequence is a functional human telomere.The human genome contains a variety of DNA sequences present in multiple copies (1). These repetitive DNA sequences are thought to arise by many mechanisms, from direct sequence amplification by the unequal recombination of homologous DNA regions to the reverse flow of genetic information (2). While it is likely that some ofthese repetitive DNA sequences influence the structure and function of the human genome, little experimental evidence supports this idea at present. We reasoned, however, that evolutionary conservation of a particular repetitive DNA sequence family might imply that the sequence is essential to cellular function. To isolate highly conserved repetitive DNA sequences, we constructed a recombinant human repetitive DNA library (pHuR library, for plasmid human repeat) and isolated clones that shared a high degree of sequence identity with rodent repetitive DNA. Four of the six most conserved cloned sequences isolated in this manner consisted of tandem arrays of the alternating (dG-dT)-(dA-dC) sequence, known to be ubiquitously interspersed in eukaryotic genomes and capable of forming the alternative Z-DNA conformation (3).The remaining two highly conserved cloned DNA sequences consisted of tandem arrays of the hexanucleotide sequence (TTAGGG), ¶ identical to the hexanucleotide sequence known to be at the telomeres of trypanosome chromosomes (4, 5). A telomere is functionally defined as a region of DNA at the molecular end of a linear chromosome that is required for replication and stability of the chromosome (6). Replicating a linear DNA molecule presents unique challenges, since all known DNA polymerases require a polynucleotide primer bearing a 3'-hydroxyl group. A variety of mechanisms are used to circumvent this replication problem, from the production of concatemeric genomes (7) to the evolution of specific telomere terminal transferase enzymes (8). In addition to their role in chromosome replication, functional telomeric DNA sequences are believed to confer stability to chromosomes, preventing the end-to-end fusions and DNA degradation normally observed after breakage of chromosomes by x-irradiation or physical rupture (6).In this paper, we present the results of fluorescent in situ hybridization (9) and BAL-31 nuclease digestion experiments (4, 5), ...

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Whilst plastics have played an instrumental role in human development, growing environmental concerns have led to increasing public scrutiny and demands for outright bans. This has stimulated considerable research into renewable alternatives, and more recently, the development of alternative waste management strategies. Herein, the aim was to highlight recent developments in the catalytic chemical recycling of two commercial polyesters, namely poly(lactic acid) (PLA) and poly (ethylene terephthalate) (PET). The concept of chemical recy-cling is first introduced, and associated opportunities/challenges are discussed within the context of the governing depolymerisation thermodynamics. Chemical recycling methods for PLA and PET are then discussed, with a particular focus on upcycling and the use of metal-based catalysts. Finally, the attention shifts to the emergence of new materials with the potential to modernise the plastics economy. Emerging opportunities and challenges are discussed within the context of industrial feasibility.

A nasopharyngeal carcinoma tumour (designated C15) propagated in nude mice has been used to generate a large cDNA library that we have analysed for Epstein‐Barr virus (EBV) gene expression. No gross alterations exist in viral DNA from C15 relative to other human isolates and the large deletion present in the B95‐8 ‘prototype’ viral strain established in marmoset cells is not found; C15 contains no linear virion DNA. In the cDNA library, of the six EBV nuclear antigens (EBNAs) expressed in latently infected B‐lymphocytes, only clones for EBNA‐1 are found. These data are confirmed by immunoblotting. Sequence analysis shows the EBNA‐1 mRNA splicing pattern in the carcinoma to differ from that observed in B‐lymphocytes. Further, contrary to observations with B‐cell lines, most viral transcription in the tumour is localized onto the ‘rightmost’ region of the conventional EBV physical map. Transcripts identified corresponding to known genes include those for the latent membrane protein (LMP), the alkaline DNA exonuclease and probably the terminal protein; major transcripts are also derived from the BamHI D fragment and the region deleted in B95‐8 EBV DNA. Novel transcripts have also been identified that proceed in an anti‐sense direction to genes encoding functions associated with replication, such as the viral DNA polymerase. They contain a large, hitherto unidentified, open reading frame in the viral genome that is complementary to the putative function known as BALF3 and a smaller open reading frame complementary to BALF5 (the DNA polymerase gene). From the present studies we can conclude that: (i) EBV transcription patterns in the epithelial cells vary markedly from those identified previously in B‐cells, reflecting differential use of promoters or splicing patterns. (ii) Transcription is tightly regulated and restricted in the C15 tumour with many latent genes, notably EBNAs 2‐6, being ‘switched off.’ (iii) A family of cytoplasmic RNAs are transcribed in an antisense direction to a number of existing open reading frames in the EBV genome. (iv) There are a number of mutations in C15 transcripts relative to the B95‐8 genome, some of which could result in amino acid alterations in proteins.

The COP9 signalosome (CSN) is a central component of the activation and remodelling cycle of cullin-RING E3 ubiquitin ligases (CRLs), the largest enzyme family of the ubiquitin–proteasome system in humans. CRLs are implicated in the regulation of numerous cellular processes, including cell cycle progression and apoptosis, and aberrant CRL activity is frequently associated with cancer. Remodelling of CRLs is initiated by CSN-catalysed cleavage of the ubiquitin-like activator NEDD8 from CRLs. Here we describe CSN5i-3, a potent, selective and orally available inhibitor of CSN5, the proteolytic subunit of CSN. The compound traps CRLs in the neddylated state, which leads to inactivation of a subset of CRLs by inducing degradation of their substrate recognition module. CSN5i-3 differentially affects the viability of tumour cell lines and suppresses growth of a human xenograft in mice. Our results provide insights into how CSN regulates CRLs and suggest that CSN5 inhibition has potential for anti-tumour therapy.