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Topoisomerase I (topo I) is required for releasing torsional stress during simian virus 40 (SV40) DNA replication. Recently, it has been demonstrated that topo I participates in initiation of replication as well as in elongation. Although T antigen and topo I can bind to one another in vitro, there is no direct evidence that topo I is a component of the replication initiation complex. We demonstrate in this report that topo I associates with T-antigen double hexamers bound to SV40 origin DNA (T DH ) but not to single hexamers. This association has the same nucleotide and DNA requirements as those for the formation of double hexamers on DNA. Interestingly, topo I prefers to bind to fully formed T DH complexes over other oligomerized forms of T antigen associated with the origin. High ratios of topo I to origin DNA destabilize T DH . The partial unwinding of a smallcircular-DNA substrate is dependent on the presence of both T antigen and topo I but is inhibited at high topo I concentrations. Competition experiments with a topo I-binding fragment of T antigen indicate that an interaction between T antigen and topo I occurs during the unwinding reaction. We propose that topo I is recruited to the initiation complex after the assembly of T DH and before unwinding to facilitate DNA replication.The mechanism of initiation of eukaryotic DNA replication is not yet clearly understood. To study this process, currently the best model systems are those of simian virus 40 (SV40) and other small DNA tumor viruses. SV40 DNA replication initiates from a well-defined single origin. The core of the origin consists of three parts, a central region known as site II (which consists of four GAGGC pentanucleotide repeats), an AT-rich track, and an early palindrome (EP) region (14). This 64-bplong core is sufficient for SV40 DNA replication (15), but the efficiency of replication is enhanced by auxiliary regions on both sides of the core, especially in vivo (23).The large tumor (T) antigen is the only viral protein essential for SV40 DNA replication, while the host cells provide all other required factors (33,34,56,62). The initiation of SV40 DNA replication is a multistep event. In the presence of ATP, T antigen specifically interacts with the core of the origin and assembles into a double-hexamer structure (T DH ) (12,30,36,61). This causes partial melting of the EP region and untwisting at the AT track of the origin (3,4,5,7,13,45,47). This T DH complex appears to be the basic frame around which the replication initiation complex forms, and T DH is the functional helicase during elongation (53,54,61).At least 10 cellular proteins have been identified to be essential for complete replication of SV40 DNA (33,34,56,62). Among them, DNA polymerase ␣/primase, replication protein A (RPA), and topoisomerase I (topo I) are believed to participate in DNA replication at a very early stage (19,21,37,40,41,51,57,59,63,64,65,67). Topo I is a critical enzyme needed to release the topological stress created by DNA unwinding. RPA is required to stab...

Wireless sensor-actuator networks (WSANs) are being adopted in process industries because of their advantages in lowering deployment and maintenance costs. While there has been significant theoretical advancement in networked control design, only limited empirical results that combine control design with realistic WSAN standards exist. This paper presents a cyberphysical case study on a wireless process control system that integrates state-of-the-art network control design and a WSAN based on the WirelessHART standard. The case study systematically explores the interactions between wireless routing and control design in the process control plant. The network supports alternative routing strategies, including single-path source routing and multi-path graph routing. To mitigate the effect of data loss in the WSAN, the control design integrates an observer based on an Extended Kalman Filter with a model predictive controller and an actuator buffer of recent control inputs. We observe that sensing and actuation can have different levels of resilience to packet loss under this network control design. We then propose a flexible routing approach where the routing strategy for sensing and actuation can be configured separately. Finally, we show that an asymmetric routing configuration with different routing strategies for sensing and actuation can effectively improve control performance under significant packet loss. Our results highlight the importance of co-joining the design of wireless network protocols and control in wireless control systems. * The first two authors contributed equally to this work.

In this paper, a color image encryption is proposed based on the dynamic DNA and the 4-D memristive hyper-chaos. First, chaotic matrices are generated from the 4-D memristive hyper-chaos by using the plain image, the salt key, and control parameters. Second, the dynamic encoding process is performed on three components of the plain image to obtain three DNA matrices. Third, to enhance both the security and robustness of encrypted image, dynamic confusion and diffusion are applied to the encoded DNA matrices. Finally, the encrypted image is generated by DNA decoding and components combining. The main feature of our proposed algorithm is that dynamic DNA mechanism based on hyper-chaos is performed on the processes of encoding, confusion, and diffusion. Simulation results and security analysis further demonstrate that it has a strong resistance against various attacks and outperforms other methods in the literature. INDEX TERMS Dynamic DNA, color image, encryption, memristive hyper-chaos.