Genomic Organization of the Human Skeletal Muscle Sodium Channel Gene

Voltage-dependent sodium channels are essential for normal membrane excitability and contractility in adult skeletal muscle. The gene encoding the principal sodium channel α-subunit isoform in human skeletal muscle (SCN4A) has recently been shown to harbor point mutations in certain hereditary forms of periodic paralysis. We have carried out an analysis of the detailed structure of this gene including delineation of intron-exon boundaries by genomic DNA cloning and sequence analysis. The complete coding region of SCN4A is found in 32.5 kb of genomic DNA and consists of 24 exons (54 to > 2.2 kb) and 23 introns (97 bp-4.85 kb). The exon organization of the gene shows no relationship to the predicted functional domains of the channel protein and splice junctions interrupt many of the transmembrane segments. The genomic organization of sodium channels may have been partially conserved during evolution as evidenced by the observation that 10 of the 24 splice junctions in SCN4A are positioned in homologous locations in a putative sodium channel gene in Drosophila (para). The information presented here should be extremely useful both for further identifying sodium channel mutations and for gaining a better understanding of sodium channel evolution.     

Expression of p21ras-related protein in the plasma and tissue of patients with adenomas and carcinomas of the colon

Over-expression of p21 ras-related protein was determined in the plasma by immunoblotting and in the tissue by immuno-histochemistry in a cohort of patients undergoing colonoscopy. In the plasma samples, p21 ras over-expression was detected in: 9% (4/47) of normal controls; 21% (13/61) of individuals with normal colonoscopies but with a prior history of colonic neoplasia; 12% (4/33) of small adenoma patients, 29% (6/21) of large adenoma patients; 63% (5/8) of carcinoma-in-adenoma patients; 50% (2/4) of Dukes' A carcinoma patients; and 20% (2/10) of Dukes' B-D carcinoma patients. In the tissue samples, p21 ras over-expression was detected in: 25% (2/8) of small adenoma patients; 44% (4/9) of large adenoma patients; 100% (4/4) of carcinoma-in-adenoma patients; and 33% (1/3) of Dukes' B-C carcinoma patients. For matched plasma-tissue pairs, there was a statistically significant correlation for p21 ras over-expression (R = 0.47, p = 0.02).     

Characterization of two mannose-binding protein cDNAs from rhesus monkey (Macaca mulatta): structure and evolutionary implications

Mannose-binding proteins (MBPs), members of the collectin family,have been implicated as lectin opsonins for various virusesand bacteria. Two distinct but related MBPs, MBP-A and MBP-C,with -55% identity at the amino acid level, have been previouslycharacterized from rodents. In humans, however, only one formof MBP has been characterized. In this paper we report studieselucidating the evolution of primate MBPs. ELISA and Westernblot analyses indicated that rhesus and cynomolgus monkeys havetwo forms of MBP in their sera, while chimpanzees have onlyone form, similar to humans. Two distinct MBP cDNA clones wereisolated and characterized from a rhesus monkey liver cDNA library.Rhesus MBP-A is closely related to the mouse and rat MBP-A,showing 77% and 75% identity at the amino acid level, respectively.Rhesus MBP-A also has three cysteines at the N-terminus, similarto mouse and rat MBP-A and human MBP. Rhesus MBP-C shares 90%identity with the human MBP at the amino acid level and hasthree cysteines at the N-terminus, in contrast to two cysteineresidues found in rodent MBP-C. A stretch of nine amino acidsclose to the N-terminus, absent in both mouse and rat MBP-A,but present in rodent MBP-C, chicken and human MBPs, is alsofound in the rhesus MBP-A. The phylogenetic analysis of rhesusand other mammalian MBPs, coupled with the serological datasuggest that at least two distinct MBP genes existed prior tomammalian radiation and the hominoid ancestor apparently lostone of these genes or failed to express it. collectin rhesus monkey mannose-binding protein MBP cDNA mannan-binding protein     

Sequential assignment of 1H, 13C and 15N resonances of human carbonic anhydrase I by triple-resonance NMR techniques and extensive amino acid-specific 15N-labeling

Summary The backbone NMR resonances of human carbonic anhydase I (HCA I) have been assigned. This protein is one of the largest monomeric proteins assigned so far. The assignment was enabled by a combination of 3D triple-resonance experiments and extensive use of amino acid-specific ¹⁵N-labeling. The obtained resonance assignment has been used to evaluate the secondary structure elements present in solution. The solution structure appears to be very similar to the crystal structure, although some differences can be observed. Proton-deuteron exchange experiments have shown that the assignments provide probes that can be used in future folding studies of HCA I.The chemical shift data have been deposited in the BioMagResBank in Madison, WI, U.S.A.     

Tuning of electron delocalization in polynuclear mixed-valence clusters by super-exchange and double exchange

 Values for the exchange-coupling constant J and the double-exchange parameter B have been estimated for dimeric and hexameric mixed-valence iron clusters. For sulfur-bridged species the range of J values is 300–450 cm^–1, and B values vary between 320 and 400 cm^–1. For an OH-bridged diiron cluster B is as large as 1300 cm^–1. Received and accepted: 23 January 1996     

Striga hermonthica decreases photosynthesis in Zea mays through effects on leaf cell structure

Maize seedlings were grown in pots either with or without preconditionedseeds of the parasitic weed, Striga hermonthica. After between4 and 8 weeks, net photosynthesis in the leaves of maize plantsinfected with Striga decreased compared to leaves of uninfectedcontrol plants. The activities of four enzymes of photosyntheticmetabolism were, however, little affected by infection. A pulse-chaseexperiment using ¹⁴CO₂ showed that C₄ acids were the main earlyproducts of assimilation even when the rate of photosynthesiswas much decreased by infection, but more radio-activity appearedin glycine and serine than in leaves of healthy maize plants.Leaves of infected maize required longer to reach a steady rateof photosynthesis upon enclosure in a leaf chamber than leavesof uninfected plants after similar treatment. Electron microscopy of transverse sections of the leaves ofinfected maize indicated that the cell walls in the bundle sheathand vascular tissue were less robust than in leaves of healthyplants. The results suggest that infection with Striga causesan increase in the permeability of cell walls in the bundlesheath, leakage of CO₂ from the bundle sheath cells and decreasedeffectiveness of C₄ photosynthesis in host leaves. Key words: Zea mays, Striga hermonthica, photosynthesis, photorespiration, enzyme activity     

Selection for non-diapause inAmblyseius cucumeris andAmblyseius barkeri and exploration of the effectiveness of selected strains for thrips control

In Europe and North America the western flower thrips,Frankliniella occidentalis, is an important pest in various greenhouse crops, such as sweet pepper and cucumber. Two species of predatory mite are commercially applied for biological control of this pest:Amblyseius cucumeris andA. barkeri. Thrips control is generally successful from March onwards. During winter, however, thrips control by these predatory mites is less effective. An important reason for this is that the commercially applied strains of both mite species enter reproductive diapause under short-day photoperiods, whereas the western flower thrips does not enter diapause. In this paper we report on selection experiments for non-diapause in strains of both mite species, aimed at obtaining predators that do not enter diapause under light- and temperature conditions prevailing in winter. Additional experiments were done to estimate the potential of the selected lines as control agents ofF. occidentalis. Selection for non-diapause proved highly successful in both predatory mite species. In a New Zealand strain ofA. cucumeris diapause incidence decreased from 41% to 0% in about ten generations; in a Dutch strain ofA. barkeri diapause incidence decreased from 67% to 0% in about six generations. Furthermore, selection for non-diapause had no influence on predator performance, measured as predation rate and oviposition rate on a diet of first instar thirps larvae. Rates of predation and oviposition were the same for selected and unselected lines in both species; rates of predation and oviposition were higher forA. cucumeris than forA. barkeri. After 18 months under non-diapause conditions, no less than 92% of a sample of the selected non-diapause line ofA. cucumeris did not enter diapause when tested under diapause-inducing conditions. This indicates that ‘non-diapause’ is a stable trait in these predatory mites. Finally, a small-scale greenhouse experiment in a sweet pepper crop showed that the selected non-diapause line ofA. cucumeris established successfully under diapause-inducing short-day conditions.