Interruption-deficient mutants of bacteriophage T5 I. Isolation and general properties.

Mutations of bacteriophage T5 were isolated which lack one or more of the natural single-chain interruptions that occur in the mature DNA of this virus. Interruption-deficient mutants were detected by screening survivors of hydroxylamine mutagenesis for altered DNA structure by electrophoresis in agarose slab gels. Over 60 independent mutants were isolated from a survey of approximately 800 phages particles. All of the mutants were viable and could be grouped into two classes. Mutants in one class lacked one of the localized sites where interruptions occur in T5 DNA. To date, mutants that affect five different sites have been obtained. Mutants in the other class were essentially free from interruptions or had a reduced frequency of interruptions throughout the genome. The members of this class included several amber mutants. Complementation tests indicated that at least two genes are required for the presence of interruptions in mature T5 DNA.     

Freeze-fracturing in normal vacuum reveals ringlike yeast plasmalemma structures

The fine structure of the regular arrays of subunits seen on both plasmalemma fracture faces in resting and starved Saccharomyces cerevisiae (baker's yeast) has been compared using different freeze-fracture replication methods. Freeze-cleaving was carried out at 173 degrees, 133 degrees, and 108 degrees K under a vacuum of 2 X 10(-7) torr (2.6 X 10(- 7)mbar) or under liquid nitrogen at atmosphereic pressure. Independent of the preparation conditions (fracturing temperature, and whether cleaved under vacuum or liquid nitrogen), resting and starved yeast show a significant difference in the morphology of the subunits forming the regular arrays. The regularly arranged particles of the P face of the plasmalemma of starved yeast have a clear craterlike structure which has previously been reported to be demonstrated only by freeze-etching at very low temperatures in ultrahigh vacuum. A complementary structure is seen on the plasmalemma E face. Prolonged exposures of fracture faces under the protection of liquid nitrogen-cooled shrouds have shown that, because of the consequent drastic reduction of condensable gases in the specimen area, no detectable condensation contamination of exposed fracture faces occurs within 15 min at a specimen temperature of 108 degrees K. This shows that a complicated ultrahigh vacuum technology is not required for high resolution freeze- etching.     

Spectroscopic evidence for the uneven distribution of adenine and uracil residues in ribosomal ribonucleic acid of Drosophila melanogaster and of Plasmodium knowlesi and its possible evolutionary significance.

RNA was isolated from subribosomal particles of the malaria parasite Plasmodium knowlesi. The nucleotide composition (mole fraction) of the principal species was obtained (S-rRNA, 0.295A, 0.36U, 0.25G, 0.105C: L-rRNA, 0.326A, 0.31U, 0.228G, 0.144C). Ribosomal RNA was also isolated from Drosophila melanogaster. Optical properties of these A + U-rich species were measured. In all four cases analysis of the hypochromic effect revealed that adenine and uracil residues tended to form clusters along the polynucleotide chain. A substantial fraction of residues was located in bihelical regions of approx. 50% G-C base pairs or in regions of approx. 30-35% G-C base pairs. The possible evolutionary significance of these results was considered on the basis of comparison with properties of rRNA from bacteria (Escherichia coli) and a mammal (rabbit reticulocyte).     

Biosafety considerations of RNAi-mediated virus resistance in fruit-tree cultivars and in rootstock

A major application of RNA interference (RNAi) is envisaged for the production of virus-resistant transgenic plants. For fruit trees, this remains the most, if not the only, viable option for the control of plant viral disease outbreaks in cultivated orchards, due to the difficulties associated with the use of traditional and conventional disease-control measures. The use of RNAi might provide an additional benefit for woody crops if silenced rootstock can efficiently transmit the silencing signal to non-transformed scions, as has already been demonstrated in herbaceous plants. This would provide a great opportunity to produce non-transgenic fruit from transgenic rootstock. In this review, we scrutinise some of the concerns that might arise with the use of RNAi for engineering virus-resistant plants, and we speculate that this virus resistance has fewer biosafety concerns. This is mainly because RNAi-eliciting constructs only express small RNA molecules rather than proteins, and because this technology can be applied using plant rootstock that can confer virus resistance to the scion, leaving the scion untransformed. We discuss the main biosafety concerns related to the release of new types of virus-resistant plants and the risk assessment approaches in the application of existing regulatory systems (in particular, those of the European Union, the USA, and Canada) for the evaluation and approval of RNAi-mediated virus-resistant plants, either as transgenic varieties or as plant virus resistance induced by transgenic rootstock.     

Microsatellite Analysis of Oil Palms and their Progenies Bred in Papua New Guinea

Our aim was to assess parental and population genetic variability in a partially nested set of breeding populations from the breeding program at Dami Research Station (West New Britain, PNG). Twenty microsatellite markers were tested for their ability to characterize genetic variation in oil palm populations bred at Dami Research Station. One hundred and twenty six individuals, including 100 F₁ tenera hybrids of Dami Deli crossed with either AVROS, Ghana or AVROS/Ghana breeding lines were analysed. Eighteen of these markers were polymorphic within and among populations, amplifying 103 alleles in oil palm. Three individuals of other palm species (Cocos nucifera and two Phoenix spp.) were included as outliers. With these markers we have the power to distinguish individual palms, hence we conclude that they will facilitate association of markers with important phenotypic traits to streamline future breeding and selection.     

Mechanism of Action of Secreted Newt Anterior Gradient Protein

Anterior gradient (AG) proteins have a thioredoxin fold and are targeted to the secretory pathway where they may act in the ER, as well as after secretion into the extracellular space. A newt member of the family (nAG) was previously identified as interacting with the GPI-anchored salamander-specific three-finger protein called Prod1. Expression of nAG has been implicated in the nerve dependence of limb regeneration in salamanders, and nAG acted as a growth factor for cultured newt limb blastemal (progenitor) cells, but the mechanism of action was not understood. Here we show that addition of a peptide antibody to Prod1 specifically inhibit the proliferation of blastema cells, suggesting that Prod1 acts as a cell surface receptor for secreted nAG, leading to S phase entry. Mutation of the single cysteine residue in the canonical active site of nAG to alanine or serine leads to protein degradation, but addition of residues at the C terminus stabilises the secreted protein. The mutation of the cysteine residue led to no detectable activity on S phase entry in cultured newt limb blastemal cells. In addition, our phylogenetic analyses have identified a new Caudata AG protein called AG4. A comparison of the AG proteins in a cell culture assay indicates that nAG secretion is significantly higher than AGR2 or AG4, suggesting that this property may vary in different members of the family.     

Paucity of HPV-Related Head and Neck Cancers (HNC) in Nigeria

IntroductionThe burden of HPV-related Head and Neck Cancers (HNC) has been rising in the U.S. and other developed countries but this trend has not been reported in Africa. Objective of study was to evaluate the prevalence of HPV infection in HNC cancer cases seen between 1990 and 2011 at the tertiary health care institutions in Nigeria.MethodsWe retrieved 149 head and neck cancer formalin fixed, paraffin embedded tumor specimens diagnosed between 1990 and 2011 from four teaching hospitals in Nigeria. One hundred and twenty-three blocks (83%) contained appropriate HNC for analysis while DNA extraction was successful in 60% (90/149). PCR amplification was successful in 33% (49/149) and Linear Array genotyping for HPV was successful in 11% (17/149) of these cases. These were in tumors from the larynx (6), cervical lymph nodes (3), nasal cavity (2), parotid (1), palate (1), maxillary sinus (1) and mandible (1). Two cases were non-specific and none were from the oropharynx. Histologically, 41% (7/17) of the successfully genotyped blocks were squamous cell carcinomas (larynx 6, maxillary sinus 1).

Results and Conclusion

We were unable to detect HPV in any of the HNC samples in our study. Our result may suggest that there is a low prevalence of HPV-related HNC among the adult population in Nigeria. Our results provide a benchmark to compare future incidence of HPV -related HNC in this community in future. We had significant analytical challenges from possible poor tissue processing and urge that future studies should prospectively collect samples and ensure high quality sample processing.