Synthesis of 3,6-bicyclolides: a novel class of macrolide antibiotics

The synthesis of 3,6-bicyclolides from erythromycin A oxime is described. This novel class of bridged bicyclic macrolides demonstrates potent in vitro and in vivo activities against a broad spectrum of bacteria including resistant respiratory tract pathogens.     

中国野生大豆的遗传多样性和生态特异性分析

野生大豆（Glycine soja）是栽培大豆的祖先,为东亚特有种,大部分分布在中国。我们采用52对SSR引物和10个植物学性状,以遗传丰富度和Simpson多样性指数为指标,对来自中国3个地理生态区域涉及24个省区的196份野生大豆所构成的代表性样本的遗传变异进行了研究,以期从分子水平和表型水平两个层面上揭示中国野生大豆遗传多样性和地理生态特异性。结果表明：中国野生大豆群体SSR位点的等位基因平均丰富度（NA）和平均Simpson多样性指数（H）分别为16.1和0.852,高于栽培大豆（NA=11.4,H=0.773）,野生群体的遗传多样性明显高于栽培群体。3个地理生态群体中南方群体多样性最高（NA=12.9,H=0.842）,黄淮海群体最低（NA=11.4,H=0.805）,东北群体居中（NA=12.5,H=0.834）。群体间存在遗传分化,不同群体具有不同的特异等位基因,位点AW132402（A2连锁群）、Satt522（F）、satt150（M）、Sat_332（D1a）、Satt046（K）、sct_190（K）等的一些等位基因只在特定群体出现,表现出群体分化后的生态特异性。中国野生大豆植物学性状的群体变异丰富,平均Simpson多样性指数为0.710。地理群体间存在分化,最明显的是生育期性状的分化,反映了地理、光照和温度等生态因子的选择作用,其中南方地理群体多样性最高（H=0.671）。SSR分子标记和植物学性状所获结果相对一致,表明中国野生大豆地理群体间性状分化有其遗传分化的基础。     

Genome plasticity in Streptomyces: identification of 1 Mb TIRs in the S. coelicolor A3(2) chromosome

The chromosomes of several widely used laboratory derivatives of Streptomyces coelicolor A3(2) were found to have 1.06 Mb inverted repeat sequences at their termini (i.e. long-terminal inverted repeats; L-TIRs), which are 50 times the length of the 22 kb TIRs of the sequenced S. coelicolor strain M145. The L-TIRs include 1005 annotated genes and increase the overall chromosome size to 9.7 Mb. The 1.06 Mb L-TIRs are the longest reported thus far for an actinomycete, and are proposed to represent the chromosomal state of the original soil isolate of S. coelicolor A3(2). S. coelicolor A3(2), M600 and J1501 possess L-TIRs, whereas approximately half the examined early mutants of A3(2) generated by ultraviolet (UV) or X-ray mutagenesis have truncated their TIRs to the 22 kb length. UV radiation was found to stimulate L-TIR truncation. Two copies of a transposase gene (SCO0020) flank 1.04 Mb of DNA in the right L-TIR, and recombination between them appears to generate strains containing short TIRs. This TIR reduction mechanism may represent a general strategy by which transposable elements can modulate the structure of chromosome ends. The presence of L-TIRs in certain S. coelicolor strains represents a major chromosomal alteration in strains previously thought to be genetically similar.     

Targeting of the yeast Ty5 retrotransposon to silent chromatin is mediated by interactions between integrase and Sir4p

The Ty5 retrotransposons of Saccharomyces cerevisiae integrate preferentially into regions of silent chromatin at the telomeres and silent mating loci (HMR and HML). We define a Ty5-encoded targeting domain that spans 6 amino acid residues near the C terminus of integrase (LXSSXP). The targeting domain establishes silent chromatin when it is tethered to a weakened HMR-E silencer, and it disrupts telomeric silencing when it is overexpressed. As determined by both yeast two-hybrid and in vitro binding assays, the targeting domain interacts with the C terminus of Sir4p, a structural component of silent chromatin. This interaction is abrogated by mutations in the targeting domain that disrupt integration into silent chromatin, suggesting that recognition of Sir4p by the targeting domain is the primary determinant in Ty5 target specificity.     

Transformation of the host-selective toxin destruxin B by wild crucifers: probing a detoxification pathway

The destruxin B detoxification pathway present in Sinapis alba is also present in three unrelated species, Camelina sativa, Capsella bursa-pastoris, and Eruca sativa, suggesting a conservation of this pathway across crucifers. The chemical structure of a destruxin B metabolite, (6'-O-malonyl)hydroxydestruxin B beta-D-glucopyranoside, was also establised. Considering that Camelina sativa and Capsella bursa-pastoris detoxify destruxin B and produce the phytoalexins camalexins, these wild crucifers appear to represent unique and perhaps useful sources of blackleg resistance in strategic plant breeding.     

Diversity of chloroplast DNA SSRs in wild and cultivated soybeans: evidence for multiple origins of cultivated soybean

Soybean [ Glycine max (L.) Merr.] is one of the major crops in the world and was domesticated from a wild progenitor, Glycine soja Sieb. & Zucc., in East Asia. In order to address the questions concerning the evolution and maternal lineage of soybean, we surveyed the variation in chloroplast DNA simple sequence repeats (cpSSR) of 326 wild and cultivated soybean accessions that were collected from various Asian countries. Twenty-three variants were detected at six cpSSRs in the accessions tested. All of the variants were found in wild soybean, whereas only 14 variants existed in the cultigen. Combining the variants at the six cpSSRs gave 52 haplotypes in the former and eight haplotypes in the latter. Both analyses indicated a considerably higher genetic diversity in the wild soybean. Around 75% of the cultivated accessions tested possessed a common haplotype (no. 49), which was detected in only seven wild accessions, six from southern Japan and one from southern China. The predominant haplotype in the cultigen may therefore have originated from a rare haplotype of the wild soybean that is presently distributed in the southern areas of Japan and China. The remaining seven haplotypes in the cultigen were distributed regionally, and except for three rare haplotypes, largely overlapped with the distributions of wild accessions with the same respective haplotypes. Our results strongly suggest that the cultivated soybeans with different cpDNA haplotypes originated independently in different regions from different wild gene pools and/or hybrid swarms between cultivated and wild forms.