一类曲线的定义域(英文)

设K为代数闭域k的有限生成扩域.C:f(x)=ayn为K上曲线,其中f是k上至少有3个单零点的多项式且n>3是正整数,n不是域k的特征的倍数,再设a■Kn,那么曲线C不能定义在k上,即曲线C:(x)=ayn不会k(a)同构于一条k上的曲线.

Bioinformatics Analysis and Homology Modeling Study of Protein Disulfide Isomerase(mPDI) from Medicago sativa L.

pdi gene from Medicago sativa L. ,encoding Protein Disulfide Isomerase（ mPDI ）, has been cloned and sequenced. According to the mRNA and amino acid sequence, the character of mPDI such as the physical and chemical properties, hydrophilicity/hydrophobicity, signal peptide, secondary structure, coiled coil, transmembrane domains, O-glycogylation site, active site, subcellular localization, functional structural domains and three-dimensional structure were analyzed by a series of bioinformatics software. The results showed that mPDI was a hydrophobic and stable protein with 3 coiled coils, 30-glycogylation sites, 2 structural domains of thioredoxin, 2 active sites of thioredoxin, and located in rough endoplasmic reticulum. It has 512 amino acids, the theoretical pl is 4.98, and signal peptide located in 1-24AA. In the secondary structure, a-helix, random coil, extended chain is 26.37%, 53.32%, 20.31% respectively. The validation of modeling accords with the stereochemistry.

Structural insights into a novel histone demethylase PHF8

Dynamic regulation of histone methylation/demethylation plays an important role during development. Mutations and truncations in human plant homeodomain （PHD） finger protein 8 （PHF8） are associated with X-linked mental retardation and facial anomalies, such as a long face, broad nasal tip, cleft lip/cleft palate and large hands, yet its molecular function and structural basis remain unclear. Here, we report the crystal structures of the catalytic core of PHF8 with or without α-ketoglutarate （α-KG） at high resolution. Biochemical and structural studies reveal that PHF8 is a novel histone demethylase specific for di- and mono-methylated histone H3 lysine 9 （H3K9me2/1）, but not for H3K9me3. Our analyses also reveal how human PHF8 discriminates between methylation states and achieves sequence specificity for methylated H3K9. The in vitro demethylation assay also showed that the F279S mutant observed in clinical patients possesses no demethylation activity, suggesting that loss of enzymatic activity is crucial for pathogenesis of PHF8 patients. Taken together, these results will shed light on the molecular mechanism underlying PHF8-associated developmental and neurological diseases.

Use of Mutual Information Arrays to Predict Coevolving Sites in the Full Length HIV gp120 Protein for Subtypes B and C

It is well established that different sites within a protein evolve at different rates according to their role within the protein; identification of these correlated mutations can aid in tasks such as ab initio protein structure, structure function analysis or sequence alignment. Mutual Information is a standard measure for coevolution between two sites but its application is limited by signal to noise ratio. In this work we report a preliminary study to investigate whether larger sequence sets could circumvent this problem by calculating mutual information arrays for two sets of drug naive sequences from the HIV gpl20 protein for the B and C subtypes. Our results suggest that while the larger sequences sets can improve the signal to noise ratio, the gain is offset by the high mutation rate of the HIV virus which makes it more difficult to achieve consistent alignments. Nevertheless, we were able to predict a number of coevolving sites that were supported by previous experimental studies as well as a region close to the C terminal of the protein that was highly variable in the C subtype but highly conserved in the B subtype.

Androgen signaling regulates the transcription of anti-Müllerian hormone via synergy with SRY-related protein SOX9A

Anti-Mullerian hormone （amh） is one of the earliest functional genes expressed during testicular differentiation. It has been suggested that androgen signaling regulates critical genes for the differentiation and development of the testis. To elucidate the exact regulatory mechanisms involved in arnh transcription mediated by androgen signaling, androgen signaling was manipulated in zebrafish by cytochrome P450 17al （cyplTal） knockout and Flutamide treatment. In cyp17a1-deficient and Flutamide-treated testes, up-regulated sry-box9a （soxga） and down-regulated amh were observed. Moreover, a physical association of the zebrafish androgen receptor （AR） and SOX9A was found. The interaction between AR and SOX9A was mediated via the DNA binding domain （DBD） of AR and the transactivation domain （TA） of SOX9A, and was further enhanced by 5-alpha dihydrotestosterone （DHT）, one of the most potent androgens. Intriguingly, together with SOX9A, androgen signaling synergistically promoted amh transcription, mainly through the proximal 1 kb of the amh promoter region. Taken together, our data demonstrate a critical mechanism underlying the direct synergy of androgen signaling and SOX9A in the regulation of amh transcription.

Structural basis for the recognition of RNA polymerase II C-terminal domain by CREPT and p15RS

CREPT and p15RS are two recently identified homologous proteins that regulate cell proliferation in an opposite way and are closely related to human cancer development. Both CREPT and pl5RS consist of an N-terminal RPR domain and a C-terminal domain with high sequence homology. The transcription enhancement by CREPT is attributed to its interaction with RNA polymerase II （Pol II）. Here we provide biochemical and structural evidence to support and extend this molecular mechanism. Through fluorescence polarization analysis, we show that the RPR domains of CREPT and pl5RS （CREPT-RPR and pI5RS-RPR） bind to different Pol II C-terminal domain （CTD） phosphoisoforms with similar affinity and specificity. We also determined the crystal structure of pl5RS-RPR. Sequence and structural comparisons with RPR domain of Rttl03, a homolog of CREPT and p l5RS in yeast, reveal structural basis for the similar binding profile of CREPT-RPR and p 15RS-RPR with Pol II CTD. We also determined the crystal structure of the C-terminal domain of CREPT （CREPT-CTD）, which is a long rod-like dimer and each monomer adopts a coiled-coil structure. We propose that dimerization through the C-terminal domain enhances the binding strength between CREPT or pl5RS with Pol II by increasing binding avidity. Our results collectively reveal the respective roles of N-terminal RPR domain and C-terminal domain of CREPT and pl5RS in recognizing RNA Pol II.