Comparing Charge Transport in Oligonucleotides: RNA:DNA Hybrids and DNA Duplexes.

Understanding the electronic properties of oligonucleotide systems is important for applications in nanotechnology, biology, and sensing systems. Here the charge-transport properties of guanine-rich RNA:DNA hybrids are compared to double-stranded DNA (dsDNA) duplexes with identical sequences. The conductance of the RNA:DNA hybrids is ∼10 times higher than the equivalent dsDNA, and conformational differences are determined to be the primary reason for this difference. The conductance of the RNA:DNA hybrids is also found to decrease more rapidly than dsDNA when the length is increased. Ab initio electronic structure and Green's function-based density of states calculations demonstrate that these differences arise because the energy levels are more spatially distributed in the RNA:DNA hybrid but that the number of accessible hopping sites is smaller. These combination results indicate that a simple hopping model that treats each individual guanine as a hopping site is insufficient to explain both a higher conductance and ß value for RNA:DNA hybrids, and larger delocalization lengths must be considered.

The Type II Secreted Lipase/Esterase LesA is a Key Virulence Factor Required for Xylella fastidiosa Pathogenesis in Grapevines.

Pierce's disease (PD) of grapevines is caused by Xylella fastidiosa (Xf), a xylem-limited gamma-proteobacterium that is responsible for several economically important crop diseases. The occlusion of xylem elements and interference with water transport by Xf and its associated biofilm have been posited as the main cause of PD symptom development; however, Xf virulence mechanisms have not been described. Analysis of the Xf secretome revealed a putative lipase/esterase (LesA) that was abundantly secreted in bacterial culture supernatant and was characterized as a protein ortholog of the cell wall-degrading enzyme LipA of Xanthomonas strains. LesA was secreted by Xf and associated with a biofilm filamentous network. Additional proteomic analysis revealed its abundant presence in outer membrane vesicles (OMVs). Accumulation of LesA in leaf regions associated positively with PD symptoms and inversely with bacterial titer. The lipase/esterase also elicited a hypersensitive response in grapevine. Xf lesA mutants were significantly deficient for virulence when mechanically inoculated into grapevines. We propose that Xf pathogenesis is caused by LesA secretion mediated by OMV cargos and that its release and accumulation in leaf margins leads to early stages of observed PD symptoms.

An engineered innate immune defense protects grapevines from Pierce disease.

We postulated that a synergistic combination of two innate immune functions, pathogen surface recognition and lysis, in a protein chimera would lead to a robust class of engineered antimicrobial therapeutics for protection against pathogens. In support of our hypothesis, we have engineered such a chimera to protect against the gram-negative Xylella fastidiosa (Xf), which causes diseases in multiple plants of economic importance. Here we report the design and delivery of this chimera to target the Xf subspecies fastidiosa (Xff), which causes Pierce disease in grapevines and poses a great threat to the wine-growing regions of California. One domain of this chimera is an elastase that recognizes and cleaves MopB, a conserved outer membrane protein of Xff. The second domain is a lytic peptide, cecropin B, which targets conserved lipid moieties and creates pores in the Xff outer membrane. A flexible linker joins the recognition and lysis domains, thereby ensuring correct folding of the individual domains and synergistic combination of their functions. The chimera transgene is fused with an amino-terminal signal sequence to facilitate delivery of the chimera to the plant xylem, the site of Xff colonization. We demonstrate that the protein chimera expressed in the xylem is able to directly target Xff, suppress its growth, and significantly decrease the leaf scorching and xylem clogging commonly associated with Pierce disease in grapevines. We believe that similar strategies involving protein chimeras can be developed to protect against many diseases caused by human and plant pathogens.

Participation of the Cowpea mosaic virus protease in eliciting extreme resistance.

Extreme resistance of Arlington line cowpea (Vigna unguiculata) to Cowpea mosaic virus (CPMV) is under control of a dominant locus designated Cpa. We transiently expressed, using Tomato bushy stunt virus (TBSV) vectors and Agrobacterium tumefaciens, in nearly isogenic Cpa/Cpa and cpa/cpa cowpea lines, sequences from RNA1, the larger of two CPMV genomic RNAs. Activation of a Cpa-specific response mapped to the CPMV 24K protease (24KPro). Mutational analysis of the 24KPro gene implicated protease activity, rather than 24KPro structure, in Cpa-mediated recognition of CPMV invasion. A 24KPro with alanine replacing the active site cysteine [24KPro(C-A)], but not wildtype 24KPro, accumulated after agroinfiltration of the corresponding binary vector constructions into Cpa/Cpa cowpea. In cpa/cpa cowpea, both protease versions accumulated, with 24KPro(C-A) in greater abundance. Thus, enzymically active 24KPro was recognized by both cowpea genotypes, but in Cpa/Cpa cowpea the suppression of 24KPro accumulation was very strong, consistent with extreme resistance to CPMV.

Health care factors related to stage at diagnosis and survival among Medicare patients with colorectal cancer.

BACKGROUND: With the growth in enrollment of Medicare patients in HMOs the effectiveness of care received by Medicare/HMO patients continues to be of concern. By considering the relationship of insurance to stage at diagnosis, this study inquires whether HMOs emphasize early diagnosis of colorectal cancer to a greater extent than FFS plans, if particular HMO types (group/nongroup models) are more successful in doing so, and how this pertains to survival. METHODS: Data for 1329 Medicare patients with colorectal cancer, diagnosed 1987 to 1993, and residing in northern California, were acquired from a population-based cancer registry. Insurance included two types of Medicare HMOs (group and nongroup model) and three fee-for-service (FFS) categories: Medicare with private supplement, Medicare/Medicaid, and Medicare only. The relationships of insurance to AJCC stage at diagnosis and of insurance to survival following diagnosis were examined, respectively, with logistic regression models and survival analysis (controlling for age, ethnicity, tumor location, educational level, sex, and hospital type). RESULTS: Likelihood of early stage colorectal cancer was greater for Medicare patients in nongroup model HMOs or having private FFS supplements than for those in group model HMOs, Medicare/Medicaid, or Medicare alone. All-cause and colorectal cancer mortality did not differ significantly among Medicare patients with group model HMO, nongroup model HMO and private FFS supplements. Medicare/Medicaid patients experienced significantly greater all-cause mortality than private FFS patients. CONCLUSIONS: Differences within this study population in early stage diagnosis of colorectal cancer and breast cancer, respectively, by type of Medicare supplemental insurance may be attributable to which preventive screening measures are included in health plan report cards.

Switching costs, price sensitivity and health plan choice.

We investigate the extent to which sensitivity to health plan premiums differs across individuals according to characteristics related to the cost of switching plans. Our results indicate substantial variation in price sensitivity related to expected health care costs: younger, healthier employees are between two and four times more sensitive to price than employees who are older and who have been recently hospitalized or diagnosed with cancer. We also find evidence of status quo bias: estimated premium elasticities are significantly higher for new hires than for incumbent employees. Simulations combining our results with actuarial data illustrate the cost implications of risk-related differences in price elasticity.