真核细胞转录系统启动T7启动子起始的研究

利用氯霉素乙酰转移酶基因（ＣＡＴ）和人低密度脂蛋白受体基因（ＬＤＬＲ）作为报道基因,根据α－鹅膏蕈碱（α－ａｍａｎｉｔｉｎ）对真核生物ＲＮＡ聚合酶的选择性抑制,分析Ｔ７噬菌体启动了为哺乳类动物细胞启动外源基因表达的机制。结果表明：真核生物ＲＮＡ聚合酶Ⅱ可启动Ｔ７启动子的转录;同时应用ＤＮＡ－蛋白质凝胶泳动技术,发现人工合成的Ｔ７启动子能与核蛋白质结合,进上步证明了哺乳类动物细胞妄动Ｔ７启动子的转录     

Role of experience and oscillations in transforming a rate code into a temporal code

In the vast majority of brain areas, the firing rates of neurons, averaged over several hundred milliseconds to several seconds, can be strongly modulated by, and provide accurate information about, properties of their inputs. This is referred to as the rate code. However, the biophysical laws of synaptic plasticity require precise timing of spikes over short timescales (<10 ms). Hence it is critical to understand the physiological mechanisms that can generate precise spike timing in vivo, and the relationship between such a temporal code and a rate code. Here we propose a mechanism by which a temporal code can be generated through an interaction between an asymmetric rate code and oscillatory inhibition. Consistent with the predictions of our model, the rate and temporal codes of hippocampal pyramidal neurons are highly correlated. Furthermore, the temporal code becomes more robust with experience. The resulting spike timing satisfies the temporal order constraints of hebbian learning. Thus, oscillations and receptive field asymmetry may have a critical role in temporal sequence learning.     

一种新型级联码

提出一种由Turbo与纠正多个随机错误的循环码构成的新型级联码,旨在用纠正多个随机错误的循环码纠正Turbo不能纠正的错误,进一步降低误码率.仿真结果表明:信噪比超过一定值后,此级联码的误码率明显低于传统的Turbo码.     

多层光盘调制码的优化

为达到光盘容量的最大化,基于多层光盘,对现有的调制码进行了优化,并对优化后可能出现的超出jitter允差问题和锁相环(PLL)时钟同步问题进行了分析并给予解决。提出了一种有别于传统的多层混合时钟同步信号获取方法,用以满足PLL稳定工作的要求,并用数理方法验证了这种方法的有效性。最后选用d=4和k=10～15作为多层并行读写光盘调制码的参数,最大码率时可提高光盘的线密度15%～23%。     

转录调节因子DEC1的研究进展

DEC1（Differentiated embryo-chondrocyte expressed gene1）是一个碱性螺旋一环一螺旋（bHLH）结构的转录因子,在软骨形成、神经发生、免疫应答、分子钟的调控、细胞分化、肿瘤的发生中起着重要的作用。DEC1还是一个缺氧调节基因,与肿瘤细胞在缺氧环境下存活密切相关,可调控肿瘤细胞生长、凋亡相关因子如缺氧诱导因子1α、转化生长因子-β、信号转导和转录激活因子、P53等的表达。DEC1还可通过调节同一家族的分子如DEC2的表达来调节细胞的功能。本文就其研究进展加以概述。     

The genome of a motile marine Synechococcus

Marine unicellular cyanobacteria are responsible for an estimated 20-40% of chlorophyll biomass and carbon fixation in the oceans. Here we have sequenced and analysed the 2.4-megabase genome of Synechococcus sp. strain WH8102, revealing some of the ways that these organisms have adapted to their largely oligotrophic environment. WH8102 uses organic nitrogen and phosphorus sources and more sodium-dependent transporters than a model freshwater cyanobacterium. Furthermore, it seems to have adopted strategies for conserving limited iron stores by using nickel and cobalt in some enzymes, has reduced its regulatory machinery (consistent with the fact that the open ocean constitutes a far more constant and buffered environment than fresh water), and has evolved a unique type of swimming motility. The genome of WH8102 seems to have been greatly influenced by horizontal gene transfer, partially through phages. The genetic material contributed by horizontal gene transfer includes genes involved in the modification of the cell surface and in swimming motility. On the basis of its genome, WH8102 is more of a generalist than two related marine cyanobacteria.     

Testing a quantum error-correcting code on various platforms

Quantum error correction plays an important role in fault-tolerant quantum information processing.It is usually difficult to experimentally realize quantum erro...     

Structural analysis of a eukaryotic sliding DNA clamp-clamp loader complex

Sliding clamps are ring-shaped proteins that encircle DNA and confer high processivity on DNA polymerases. Here we report the crystal structure of the five-protein clamp loader complex (replication factor-C, RFC) of the yeast Saccharomyces cerevisiae, bound to the sliding clamp (proliferating cell nuclear antigen, PCNA). Tight interfacial coordination of the ATP analogue ATP-gammaS by RFC results in a spiral arrangement of the ATPase domains of the clamp loader above the PCNA ring. Placement of a model for primed DNA within the central hole of PCNA reveals a striking correspondence between the RFC spiral and the grooves of the DNA double helix. This model, in which the clamp loader complex locks onto primed DNA in a screw-cap-like arrangement, provides a simple explanation for the process by which the engagement of primer-template junctions by the RFC:PCNA complex results in ATP hydrolysis and release of the sliding clamp on DNA.