Genome-wide CRISPR Screens Reveal Host Factors Critical for SARS-CoV-2 Infection

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南方菜豆花叶病毒外壳蛋白基因序列的分析

用重组DNA技术及序列分析法测定了南方菜豆花叶病毒RNA基因组3′端1,000个碱基的序列,以及由此序列推导出的整个外壳蛋白的氨基酸顺序,它与巳报导的基本上一致。介绍了用DNA的寡核苷酸水解混合物作为起始引物,以3′端不含PolyA尾巴且不能加上PolyA的病毒RNA作为模板合成互补DNA,及进一步无性繁殖此cDNA的方法。     

Picrosirius Red Staining of Cardiac Muscle Following Phosphomolybdic Acid Treatment

When the picrosirius red technique was applied to cardiac muscle sections, intense yellow myocyte staining sometimes obscured thin collagenous septa. The picrosirius red technique was modified to include treatment of the sections in 0.2% (w/v) aqueous phosphomolybdic acid prior to staining. With 1-5 min treatment, cytoplasmic staining was eradicated; diminution of collagen staining occurred only with long treatments at much higher concentrations of phosphomolybdic acid. Using this phosphomolybdic acid-picrosirius red technique, collagenous septa as thin as 0.2-0.5 /im and fine collagen fibers making up the septa were clearly discernible. The technique also worked well on sections stained by other techniques and then destained. The phosphomolybdic acid-picrosirius red technique should be useful in experiments designed to investigate the effects of collagen distribution on the electrical and mechanical behavior of cardiac muscle.     

Feedback inhibition of homoserine kinase from radish leaves

Homoserine kinase is a potential control point in the biosynthetic pathway for threonine, isoleucine and methionine. The radish leaf enzyme was tested     

Differential effects of prostaglandin E2 on contractions of airway smooth muscle

In an in vitro muscle bath, the active tension generated by strips of canine tracheal smooth muscle responding to cumulative additions of either histamine (10(-8) to 10(-3) M) or acetylcholine (10(-9) to 10(-3) M) was measured in the absence and presence of prostaglandin E2 (PGE2) (10(-6) to 10(-5) M). When contractile responses of equal magnitude were compared, the contractions elicited by acetylcholine were resistant to the inhibitory effects of PGE2, relative to comparable contractions elicited by histamine. To assess the role of adenylate cyclase in determining the different responses to histamine and acetylcholine in the presence of PGE2, we assayed adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and found that acetylcholine, but not histamine, decreased PGE2-stimulated adenylate cyclase activity by 48 +/- 2% (mean +/- SE; n = 5). However, in other experiments, we found that even large pharmacological increases in tissue adenosine 3',5'-cyclic monophosphate (cAMP) content only partially inhibited muscarinic tone. Also, exogenously applied analogues of cyclic AMP inhibited contractions induced by histamine more effectively than comparable contractions induced by acetylcholine. We concluded that acetylcholine decreased adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and that this effect may have contributed to, but did not completely account for, the relative resistance of muscarinic contractions to the inhibitory effects of PGE2.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.