Sequence and analysis of chromosome 2 of the plant Arabidopsis thaliana

Arabidopsis thaliana (Arabidopsis) is unique among plant model organisms in having a small genome (130-140 Mb), excellent physical and genetic maps, and little repetitive DNA. Here we report the sequence of chromosome 2 from the Columbia ecotype in two gap-free assemblies (contigs) of 3.6 and 16 megabases (Mb). The latter represents the longest published stretch of uninterrupted DNA sequence assembled from any organism to date. Chromosome 2 represents 15% of the genome and encodes 4,037 genes, 49% of which have no predicted function. Roughly 250 tandem gene duplications were found in addition to large-scale duplications of about 0.5 and 4.5 Mb between chromosomes 2 and 1 and between chromosomes 2 and 4, respectively. Sequencing of nearly 2 Mb within the genetically defined centromere revealed a low density of recognizable genes, and a high density and diverse range of vestigial and presumably inactive mobile elements. More unexpected is what appears to be a recent insertion of a continuous stretch of 75% of the mitochondrial genome into chromosome 2.     

A structural change in the kinesin motor protein that drives motility

Kinesin motors power many motile processes by converting ATP energy into unidirectional motion along microtubules. The force-generating and enzymatic properties of conventional kinesin have been extensively studied; however, the structural basis of movement is unknown. Here we have detected and visualized a large conformational change of an approximately 15-amino-acid region (the neck linker) in kinesin using electron paramagnetic resonance, fluorescence resonance energy transfer, pre-steady state kinetics and cryo-electron microscopy. This region becomes immobilized and extended towards the microtubule 'plus' end when kinesin binds microtubules and ATP, and reverts to a more mobile conformation when gamma-phosphate is released after nucleotide hydrolysis. This conformational change explains both the direction of kinesin motion and processive movement by the kinesin dimer.     

Oldest playable musical instruments found at Jiahu early Neolithic site in China

Excavations at the early Neolithic site of Jiahu in Henan Province, China have produced what may be the earliest complete, playable, tightly-dated multinote musical instruments. Jiahu was occupied from 7000 BC to 5700 BC, considerably antedating the well known Peiligang culture. Here we describe six exquisitely made complete flutes which were found in radiocarbon-dated excavation layers, along with fragments of perhaps 30 more. The flutes are made from the ulnae of the red-crowned crane (Grus japonensis Millen) and have 5, 6, 7 and 8 holes. The best preserved flute has been played and tonally analysed. In addition to early musical artefacts, the archaeological record at Jiahu contains important information on the very foundations of Chinese society. We describe the archaeological characteristics of the Jiahu site, details concerning its dating, its place in the prehistory of the Chinese Neolithic, the ethnicity of its population and the results of a tonal analysis of a nearly 9,000-year-old musical instrument found there.     

Functional recognition of the 3' splice site AG by the splicing factor U2AF35

In metazoans, spliceosome assembly is initiated through recognition of the 5' splice site by U1 snRNP and the polypyrimidine tract by the U2 small nuclear ribonucleoprotein particle (snRNP) auxiliary factor, U2AF. U2AF is a heterodimer comprising a large subunit, U2AF65, and a small subunit, U2AF35. U2AF65 directly contacts the polypyrimidine tract and is required for splicing in vitro. In comparison, the role of U2AF35 has been puzzling: U2AF35 is highly conserved and is required for viability, but can be dispensed with for splicing in vitro. Here we use site-specific crosslinking to show that very early during spliceosome assembly U2AF35 directly contacts the 3' splice site. Mutational analysis and in vitro genetic selection indicate that U2AF35 has a sequence-specific RNA-binding activity that recognizes the 3'-splice-site consensus, AG/G. We show that for introns with weak polypyrimidine tracts, the U2AF35-3'-splice-site interaction is critical for U2AF binding and splicing. Our results demonstrate a new biochemical activity of U2AF35, identify the factor that initially recognizes the 3' splice site, and explain why the AG dinucleotide is required for the first step of splicing for some but not all introns.     

“铅树”生成条件的研究

提出了生成“铅树”反应成功的关键是硅酸凝胶的坚固性,找到了较好的硅酸凝胶的制备条件,使该氧化还原平衡移动的反应成功率提高了９０ ％ 以上．