DNA甲基化是细菌进行表观遗传调控的重要方式,α变形菌利用受细胞周期调控的DNA甲基转移酶(cell cycle-regulated DNA methyltransferase,CcrM)对DNA进行甲基化。CcrM不含限制性内切酶功能单元,属于孤儿甲基转移酶。CcrM通过对序列中腺...DNA甲基化是细菌进行表观遗传调控的重要方式,α变形菌利用受细胞周期调控的DNA甲基转移酶(cell cycle-regulated DNA methyltransferase,CcrM)对DNA进行甲基化。CcrM不含限制性内切酶功能单元,属于孤儿甲基转移酶。CcrM通过对序列中腺嘌呤进行甲基化影响DNA与蛋白质的相互作用,从而调节大量基因的表达,对α变形菌细胞周期等过程的调控至关重要。本文综述了CcrM的功能、结构及其表观调控机制,阐明了CcrM对DNA的识别、催化及活性调控的机理,总结了细胞周期全局性调控因子(global cell-cycle regulator,GcrA)利用CcrM的甲基化信号调节基因表达的机制,并展望了CcrM未来的潜在研究方向,为进一步深入研究细菌表观遗传调控机制提供了参考。展开更多
Network calculus is an evolving new methodology for backlog and delay analysis of packet-switching networks. With network calculus we are able to compute tight bounds on delays,backlogs,and effective bandwidths in a l...Network calculus is an evolving new methodology for backlog and delay analysis of packet-switching networks. With network calculus we are able to compute tight bounds on delays,backlogs,and effective bandwidths in a lossless setting applicable to packet-switching networks and better understand some physical properties of networks. In this paper,the basic network calculus concepts of arrival curves and service curves are introduced.Then we provide the approach for modeling leaky-bucket,generic cell rate algorithm(GCRA),constant bit rate(CBR)flow, variable bit rate(VBR) flow with arrival curve.It is shown that all rate-based packet schedulers can be by a simple rate latency service curve.And by applying these fundamental rules of network calculus,bounds on delay, buffer,effective bandwidth for leaky bucket,GCRA,CBR and VBR can be derived and some practical examples are given.Finally,we compare all the results obtained and conclude this paper.展开更多
基金supported in part by the development Foundation of Southwest Jiaotong Universitythe National Natural Science Foundation of China under Grant No.60572143
文摘Network calculus is an evolving new methodology for backlog and delay analysis of packet-switching networks. With network calculus we are able to compute tight bounds on delays,backlogs,and effective bandwidths in a lossless setting applicable to packet-switching networks and better understand some physical properties of networks. In this paper,the basic network calculus concepts of arrival curves and service curves are introduced.Then we provide the approach for modeling leaky-bucket,generic cell rate algorithm(GCRA),constant bit rate(CBR)flow, variable bit rate(VBR) flow with arrival curve.It is shown that all rate-based packet schedulers can be by a simple rate latency service curve.And by applying these fundamental rules of network calculus,bounds on delay, buffer,effective bandwidth for leaky bucket,GCRA,CBR and VBR can be derived and some practical examples are given.Finally,we compare all the results obtained and conclude this paper.
