Streptomyces Linear Plasmids Replication and Telomeres

Carton W. Chen

Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Shih-Pai, 112 Taipei, Taiwan [email protected]

1 Introduction 34

1.1 Unique System of Replication 34

2 Terminal DNA 35

2.1 Archetypal Telomeres 35

2.2 Nonarchetypal Telomeres 38

2.3 Terminal Inverted Repeats 38

2.4 Pseudotelomeres 39

3 Terminal Proteins 40

3.1 Archetypal TPs 40

3.2 Nonarchetypal TPs: The TP of SCP1 42

3.3 TP-TP Interactions 43

4 Replication 44

4.1 Replication Origin and Replication Initiation 44

4.2 Elements Required for Replication in Linear Form 45

5 End Patching 46

5.1 The Mechanisms 46

5.2 Protein Players 48

5.3 DNA Templates 49

5.4 DNA Polymerase 49

6 Postreplicational Segregation 50

6.1 The Plasmid-Encoded parAB-parS System 50

6.2 Resolution of Sister Plasmids 52

7 Conjugal Transfer 54

7.1 Mode of Transfer 54

7.2 Nuclear Localization 55

8 Concluding Remarks 56

References 57

Abstract Vegetative replication of terminal protein (TP)-capped linear plasmids (and linear chromosomes) of Streptomyces proceeds in two steps: a classical bidirectional replication from an internal origin followed by a novel TP-primed DNA synthesis that patches the resulting single-strand gaps at the 3' ends ("end patching"). Replication initiation systems found on different linear Streptomyces plasmids consist of helicase-like genes and itérons of relatively diverse origins. In contrast, the end patching system (including the telomeres and the TPs) is highly conserved in most linear replicons in Streptomyces with only a single exception so far. Both the TPs and the telomeric DNAs have evolved structural features to serve replication as well as protection of the telomeres. Interaction of TPs shapes the linear replicon into a circular form, which would allow generation of biologically important superhelicity in terminal DNA, but would also create complications during postreplicational segregation of the daughter DNA. TPs may also be involved in priming initiation of replication during conjugal transfer. Like the T-DNA transfer system in Agrobacterium tumefaciens, the TPs can target themselves and the attached DNA into eukaryotic nuclei, thus suggesting a possibility of interkingdom conjugal transfer.

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