DNA G-quartets in a 1.86 A resolution structure of an Oxytricha nova telomeric protein-DNA complex.

The Oxytricha nova telomere end binding protein (OnTEBP) recognizes, binds and protects the single-stranded 3'-terminal DNA extension found at the ends of macronuclear chromosomes. The structure of this complex shows that the single strand GGGGTTTTGGGG DNA binds in a deep cleft between the two protein subunits of OnTEBP, adopting a non-helical and irregular conformation. In extending the resolution limit of this structure to 1.86 A, we were surprised to find a G-quartet linked dimer of the GGGGTTTTGGGG DNA also packing within the crystal lattice and interacting with the telomere end binding protein. The G-quartet DNA exhibits the same structure and topology as previously observed in solution by NMR with diagonally crossing d(TTTT) loops at either end of the four-stranded helix. Additionally, the crystal structure reveals clearly visible Na(+), and specific patterns of bound water molecules in the four non-equivalent grooves. Although the G-quartet:protein contact surfaces are modest and might simply represent crystal packing interactions, it is interesting to speculate that the two types of telomeric DNA-protein interactions observed here might both be important in telomere biology.     

Allometric growth and adaptive value of exaggerated body parts in the larvae of Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae)

1. Larvae of tortoise beetles present exaggerated body parts in association with an abdominal shield, which is made of faeces and exuviae that are deposited on the urogomphi throughout ontogeny. Growth trajectories and scaling relationships of these functional structures associated with the shield, if any, are unknown. 2. This study of Gratiana spadicea first tested, under field conditions, whether there is adaptive value associated with the shield regarding protection against predation and sunlight. Then, under laboratory conditions, the growth trajectory and allometric relationships among body parts were investigated, including scoli, individual and apparent furcae, and shield. The influence of food deprivation on the development of these structures was also determined. 3. Findings from previous studies were confirmed, suggesting that the adaptive value assigned to the shield is related to protection against predators. The present study demonstrated for the first time that the shield acts as a parasol in cassidines, decreasing the exposure of their larval body to sunlight. The scoli and apparent furca are exaggerated structures of G. spadicea, the development of which involves allometric growth and greater energetic investment (positive allometry) during ontogeny. There was proportionally less energetic investment for somatic construction of individual furca (negative allometry) due to the accumulation of the exuviae. 4. The possible consequences, in terms of developmental costs and survivorship benefits associated with the evolution of such exaggerated structures, are discussed.     

Host-specific regulation of nodulation genes in Rhizobium is mediated by a plant-signal, interacting with the nodD gene product

We have identified a nodD gene from the wide host-range Rhizobium strain MPIK3030 (termed nodD1) which is essential for nodulation on Macroptilium atropurpureum (siratro). Experiments with nodA–lacZ gene fusions demonstrate that the MPIK3030 nodD1 regulates expression of the nodABC genes. Additionally, we used nodC–lacZ fusions of Rhizobium meliloti to show that the MPIK3030 nodD1 gene induces expression of these fusions by interacting with plant factors from siratro and from the non-host Medicago sativa (alfalfa). The R. meliloti nodD genes, however, only interact with alfalfa exudate. In line with these results, no complementation of MPIK3030 nodD1 mutants could be obtained on siratro with the R. meliloti nodD genes, while the MPIK3030 nodD1 can complement nodD mutants of R. meliloti on alfalfa. Furthermore, R. meliloti transconjugants harbouring the MPIK3030 nodD1 efficiently nodulate the illegitimate host siratro. When compared with other nodD sequences, the amino acid sequence of the MPIK3030 nodD1 shows a conserved aminoterminus, whereas the carboxy-terminus of the putative gene product diverges considerably. Studies on a chimeric MPIK3030/R. meliloti nodD gene indicates that the carboxy-terminal region is responsible for the interaction with plant factor(s) and may have evolved in different rhizobia specifically to interact with plant–host factors.     

The inhibitory effect of succinate on radiation-enhanced mitochondrial lipid peroxidation

The degree of mitochondrial ADP/Fe/NADPH-induced lipid peroxidation was increased up to the fourth day after 9.0 Gy whole body gamma-irradiation. The lipid peroxidation inhibiting effect of succinate added to isolated mitochondria was diminished as a consequence of irradiation. The succinate, administered in vivo prior to irradiation, decreased the amount of malondialdehyde production and protected the succinate dehydrogenase enzyme against inactivation. The mean survival of succinate-pretreated animals was much longer than that of controls. The role of mitochondrial lipid peroxidation in the pathogenesis of radiation injury is discussed.     

Lipid peroxidation in Ehrlich ascites cell mitochondria is not determined by the polyunsaturated fatty acid content of the membrane

Lipid peroxidation intensity is compared in Ehrlich Ascites Cell and in liver mitochondria, prepared from tumor bearing mice. Malondialdehyde formation is negligible in intact ascites tumour mitochondria, but it is significantly increased in permeabilised mitochondria and in isolated mitochondrial membranes. We suggest that the resistance against oxidative stress is a consequence of efficient protective mechanisms operating in the intact tumour mitochondria and the low level of polyunsaturated fatty acids under these circumstances cannot be the rate limiting factor in lipid peroxidation. Succinate, an effective inhibitor of mitochondrial lipid peroxidation in liver, cannot determine malondialdehyde formation in ascites tumour mitochondria.     

Amphiphilicity is essential for mitochondrial presequence function.

We have shown earlier that a mitochondrial presequence peptide can form an amphiphilic helix. However, the importance of amphiphilicity for mitochondrial presequence function became doubtful when an artificial presequence, designed to be non-amphiphilic, proved to be active as a mitochondrial import signal. We now show experimentally that this 'non-amphiphilic' presequence peptide is, in fact, highly amphiphilic as measured by its ability to insert into phospholipid monolayers and to disrupt phospholipid vesicles. This result, and similar tests on three additional artificial presequences (two functionally active and one inactive), revealed that all active presequences were amphiphilic whereas the inactive presequence was non-amphiphilic. One of the active presequence peptides was non-helical in solution and in the presence of detergent micelles. We conclude that amphiphilicity is necessary for mitochondrial presequence function whereas a helical structure may not be essential.     

Population cytogenetics of aphidicolin-induced fragile sites

Summary Chromosome fragile sites are inducible by aphidicolin in cultured human lymphocytes. To assess the frequency and distribution of these common fragile sites in the general population, a cytogenetic survey was performed on 126 subjects, 59 males and 67 females, whose age ranged from 1 day to 72 years. Common fragile sites, induced by aphidicolin, were widespread and showed a remarkably different sensitivity among individuals; age influenced the overall frequency of fragile sites. Moreover, both age and sex seemed to modulate the expression of specific fragile sites. In our population, the most common fragile sites were: 3p14, 16q23, Xp22, 6q26, 1p31, 4q31, 1p22, 7q22, 2q33, 3q27, 2q31, 7q32, 14q24, 10q22, 5q31, 2q37, 6p21.     

Diversity of coding strategies in influenza viruses.

Influenza viruses have exploited a variety of strategies to increase their genome coding capacities. These include unspliced, spliced, alternatively spliced and bicistronic mRNAs, translation from overlapping reading frames and a coupled stop-start translation of tandem cistrons.