Structure and Replication of Vaccinia Virus Telomeres

In both prokaryotic and eukaryotic systems, DNA synthesis proceeds by the addition of deoxyribonucleotides to RNA primers (Sugino et al. 1972; Tseng and Goulian 1977). The short RNA segments are then excised, and the resulting gaps are filled in with deoxyribonucleotides. Such a mechanism can lead to the complete replication of circular DNA but does not provide a way of filling in the gap remaining at the 5′ end of a linear molecule. However, the latter step can be accomplished by the formation of circular or concatemeric replication intermediates (Watson 1972). A possible third mechanism for the replication of the ends of linear DNA molecules was suggested by Cavalier-Smith (1974), who considered that if the ends of eukaryotic DNA molecules were palindromic, they could fold back on themselves to form base-paired loops. As a simplification of this model, Bateman (1975) suggested that the telomeres of eukaryotic chromosomes might be covalently...