Stops making sense: translational trade-offs and stop codon reassignment

Background Efficient gene expression involves a trade-off between (i) premature termination of protein synthesis; and (ii) readthrough, where the ribosome fails to dissociate at the terminal stop. Sense codons that are similar in sequence to stop codons are more susceptible to nonsense mutation, and are also likely to be more susceptible to transcriptional or translational errors causing premature termination. We therefore expect this trade-off to be influenced by the number of stop codons in the genetic code. Although genetic codes are highly constrained, stop codon number appears to be their most volatile feature. Results In the human genome, codons readily mutable to stops are underrepresented in coding sequences. We construct a simple mathematical model based on the relative likelihoods of premature termination and readthrough. When readthrough occurs, the resultant protein has a tail of amino acid residues incorrectly added to the C-terminus. Our results depend strongly on the number of stop codons in the genetic code. When the code has more stop codons, premature termination is relatively more likely, particularly for longer genes. When the code has fewer stop codons, the length of the tail added by readthrough will, on average, be longer, and thus more deleterious. Comparative analysis of taxa with a range of stop codon numbers suggests that genomes whose code includes more stop codons have shorter coding sequences. Conclusions We suggest that the differing trade-offs presented by alternative genetic codes may result in differences in genome structure. More speculatively, multiple stop codons may mitigate readthrough, counteracting the disadvantage of a higher rate of nonsense mutation. This could help explain the puzzling overrepresentation of stop codons in the canonical genetic code and most variants.

Carolingian culture in the North Sea world: rethinking the cultural dynamics of personal adornment in Viking age England

Boosted by a proliferation in metal-detected finds, categories of personal adornment now constitute a vital archaeological source for interpreting Viking-age cultural interaction in the North Sea region. Previous research in England has explored the potential of this metalwork in relation to the formation of ‘Anglo-Scandinavian’ identity, but without due consideration of a wider spectrum of cultural influences. This article redresses the balance by shifting attention to twenty-eight belt fittings derived from richly embellished baldrics, equestrian equipment, and waist belts manufactured on the Frankish continent during the period of Carolingian hegemony in the later eighth and ninth centuries ad. The metalwork is classified and then contextualized in order to track import mechanisms and to assess the impact of Carolingian culture on the northern peripheries of the Frankish empire. The main conclusion is that the adoption, adaptation, and strategic manipulation of Carolingian/northern Frankish identity formed an embedded component of cultural dynamics in Viking-age England, scrutiny of which sheds new light on patterns of interconnectivity linking peoples of the North Sea world.

Mites Parasitic on Australasian and African Spiders Found in the Pet Trade; a Redescription of Ljunghia pulleinei Womersley

Parasitic mites associated with spiders are spreading world-wide through the trade in tarantulas and other pet species. Ljunghia pulleinei Womersley, a mesostigmatic laelapid mite originally found in association with the mygalomorph spider Selenocosmia stirlingi Hogg (Theraphosidae) in Australia, is redescribed and illustrated on the basis of specimens from the African theraphosid spider Pterinochilus chordatus (Gersta¨cker) kept in captivity in the British Isles (Wales). The mite is known from older original descriptions of Womersley in 1956; the subsequent redescription of Domrow in 1975 seems to be questionable in conspecificity of treated specimens with the type material. Some inconsistencies in both descriptions are recognised here as intraspecific variability of the studied specimens. The genus Arachnyssus Ma, with species A. guangxiensis (type) and A. huwenae, is not considered to be a valid genus, and is included in synonymy with Ljunghia Oudemans. A new key to world species of the genus Ljunghia is provided.

Good practice transfer within small construction specialist trade contractors

Government and institutionally-driven ‘good practice transfer’ initiatives are consistently presented as a means to enhance construction firm and industry performance. Two implicit tenets of these initiatives appear to be: knowledge embedded in good practice will transfer automatically; and, the potential of implementing good practice will be capitalised regardless of the context where it is to be used. The validity of these tenets is increasingly being questioned and, concurrently, more nuanced knowledge production understandings are being developed which recognise and incorporate context-specificity. This research contributes to this growing, more critical agenda by examining the actual benefits accrued from good practice transfer from the perspective of a small specialist trade contracting firm. A concept model for successful good practice transfer is developed from a single longitudinal case study within a small heating and plumbing firm. The concept model consists of five key variables: environment, strategy, people, technology, and organisation of work. The key findings challenge the implicit assumptions prevailing in the existing literature and support a contingency approach that argues successful good practice transfer is not just adopting and mechanistically inserting into the firm, but requires addressing ‘behavioural’ aspects. For successful good practice transfer, small specialist trade contracting firms need to develop and operationalise organisation slack, mechanisms for scanning external stimuli and absorbing knowledge. They also need to formulate and communicate client-driven external strategies; to motive and educate people at all levels; to possess internal or accessible complementary skills and knowledge; to have ‘soft focus’ immediate/mid-term benefits at a project level; and, to embed good practice in current work practices.