A model for the development of the tandem repeat units in the EBV ori-P region and a discussion of their possible function.

This paper presents an analysis of the repeat units of the ori-P region of the Epstein-Barr virus (EBV) genome. These repeat units are well-conserved palindromes. The pattern of these repeats, their lengths, phases, and the distribution of the relatively few substitutions are explained by a scenario that gives a reasonable course for the evolutionary development of the pattern. The scenario suggests a model for the production of an initiating 3/2 palindrome from a moderately lengthy sequence. The palindromic units are then multiplied in judicious combinations by mechanisms of unequal crossing-over events associated with some point substitutions and a few instances of slippage replication. The potential secondary structures of the two separated tandem palindromic repeat regions in ori-P are contrasted. Possible modes of binding of Epstein-Barr nuclear antigen (EBNA) 1 protein to these hairpins are discussed. A number of possibilities for the origin and development of the ori-P region in relation to viral and cellular function are considered.