Phylogenetic utility of the nuclear gene arginine decarboxylase: an example from Brassicaceae

Arginine decarboxylase (ADC) is an important enzyme in the production of putrescine and polyamines in plants. It is encoded by a single or low-copy nuclear gene that lacks introns in sequences studied to date. The rate of Adc amino acid sequence evolution is similar to that of ndhF for the angiosperm family studied. Highly conserved regions provide several target sites for PCR priming and sequencing and aid in nucleotide and amino acid sequence alignment across a range of taxonomic levels, while a variable region provides an increased number of potentially informative characters relative to ndhF for the taxa surveyed. The utility of the Adc gene in plant molecular systematic studies is demonstrated by analysis of its partial nucleotide sequences obtained from 13 representatives of Brassicaceae and 3 outgroup taxa, 2 from the mustard oil clade (order Capparales) and 1 from the related order Malvales. Two copies of the Adc gene, Adc1 and Adc2, are found in all members of the Brassicaceae studied to data except the basal genus Aethionema. The resulting Adc gene tree provides robust phylogenetic data regarding relationships within the complex mustard family, as well as independent support for proposed tribal realignments based on other molecular data sets such as those from chloroplast DNA.      

UGA: a dual signal for 'stop' and for recoding in protein synthesis

UGA remains an enigma as a signal in protein synthesis. Long recognized as a stop signal that is prone to failure when under competition from near cognate events, there was growing belief that there might be functional significance in the production of small amounts of extended proteins. This view has been reinforced with the discovery that UGA is found at some recoding sites where frameshifting occurs as a regulatory mechanism for controlling the gene expression of specific proteins, and it also serves as the code for selenocysteine (Sec), the 21st amino acid. Why does UGA among the stop signals play this role specifically, and how does it escape being used to stop protein synthesis efficiently at recoding sites involving Sec incorporation or shifts to a new translational frame? These issues concerning the UGA stop signals are discussed in this review.     

PiUS (Pi uptake stimulator) is an inositol hexakisphosphate kinase

A cDNA cloned from its ability to stimulate inorganic phosphate uptake in Xenopus oocytes (phosphate uptake stimulator (PiUS)) shows significant similarity with inositol 1,4,5-trisphosphate 3-kinase. However, the expressed PiUS protein showed no detectable activity against inositol 1,4,5-trisphosphate, nor the 1,3,4,5- or 3,4,5, 6-isomers of inositol tetrakisphosphate, whereas it was very active in converting inositol hexakisphosphate (InsP(6)) to inositol heptakisphosphate (InsP(7)). PiUS is a member of a family of enzymes found in many eukaryotes and we discuss the implications of this for the functions of InsP(7) and for the evolution of inositol phosphate kinases.     

Alpha-synuclein aggregation

Alpha-synuclein is a major component of Lewy bodies in Parkinson's disease and is found associated with several other forms of dementia. As with other neurodegenerative diseases, the ability of alpha-synuclein to aggregate and form fibrillar deposits seems central to its pathology. We have defined a sequence within the NAC region of alpha-synuclein that is necessary for aggregation. Exploitation of chemically modified analogues of this peptide may produce inhibitors of aggregation.     

Microsatellite DNA evidence for genetic drift and philopatry in Svalbard reindeer

Mainland populations of Arctic reindeer and caribou Rangifer tarandus often undergo extensive movements, whereas populations on islands tend to be isolated and sedentary. To characterize the genetic consequences of this difference, levels of genetic diversity and subdivision of Svalbard reindeer (R. t. platyrhynchus) from two adjacent areas on Nordenskjiöldland, Spitsbergen were estimated using data from up to 14 microsatellites. The mean number of alleles per locus in Svalbard reindeer was 2.4 and mean expected heterozygosity per locus was 0.36. The latter value was significantly lower than in Canadian caribou and Norwegian reindeer but higher than in some other cervid species. Large samples of females (n = 743) and small samples of males (n = 38) from two sites ≈ 45 km apart showed genetic subdivision, which could be due to local population fluctuations or limited gene flow. To our knowledge, this is the first study to report significant differentiation at microsatellite loci in Rangifer at such short geographical distances. Neither population showed genetic evidence for recent population bottlenecks when loci unbiased with respect to heterozygosity were analysed. In contrast, false signals of a recent bottleneck were detected when loci upwardly biased with respect to heterozygosity were analysed. Thus, Svalbard reindeer appeared to conform to the paradigm of island populations made genetically depauperate by genetic drift.     

Glycosylation regulates Notch signalling

Intracellular post-translational modifications such as phosphorylation and ubiquitylation have been well studied for their roles in regulating diverse signalling pathways, but we are only just beginning to understand how differential glycosylation is used to regulate intercellular signalling. Recent studies make clear that extracellular post-translational modifications, in the form of glycosylation, are essential for the Notch signalling pathway, and that differences in the extent of glycosylation are a significant mechanism by which this pathway is regulated.