Prokaryotes with genomes composed of linear genetic elements terminated by hairpin (hp) telomeres are typified by the spirochetes of the genus Borrelia. Amongst this genus are important human pathogens (Barbour 2001; Schwan et al. 1999) that cause Lyme borreliosis and relapsing fever maladies (Burgdorfer et al. 1982; Dworkin et al. 2002). The most extensively studied member of the species that cause Lyme borreliosis is the North American agent Borrelia burgdorferi; the best-characterized relapsing fever spirochete is the European Borrelia hermsii. Both Lyme borreliosis and relapsing fever are zoonotic diseases with complex transmission cycles between their mammalian and arthropod hosts. More recently, the plant pathogen and agro-biotechnology tool, Agrobacterium tumefaciens, has also been discovered to harbour a linear hairpin chromosome, in addition to a circular chromosome (Goodner et al. 2001).

This chapter will concentrate on B. burgdorferi, because the prototype B31 MI strain has been sequenced in its entirety and the enzyme responsible for the formation of the hp telomeres has been described. I will review what has been learned about the replication and segregation of the numerous genetic elements of this organism, as well as summarize what is known about the enzyme involved in formation of the hp telomeres.

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