Summary
The functional R6K α origin is composed of two DNA elements, one of 580 bp carrying the α origin sequences and the other of 277 bp containing the seven 22 bp direct repeats previosly identified as also required for γ and β origin activity. These two genetic elements are separated by approximately 3,000 bp of R6K sequences which are dispensable for α origin activity. The function of the α origin depends on the presence in cis of the 580 bp and the 277 bp fragments and requires that they be oriented as in the intact R6K. Activation of the α origin depends on the R6K replication initiation protein π.
Within the 580 bp of the α origin, there is a sequence of 98 bp which appears as an inverted repeat of 96 bp in the β replicon. Deletion of the 96 bp or 98 bp results in inactivation of the α and the β origins respectively. These long repeats are palindromic and it is suggested that these may serve as the recognition signals for initiation of DNA replication in the α and the β origins of R6K. DNA homology analysis performed on α, β and γ origin sequences, also reveals 10–23 bp sequences in the α and the β origins that are related to the family of 22 bp direct repeats in the γ origin which were shown previously to be binding sites for the π protein.
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Communicated by R. Devoret
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Shafferman, A., Flashner, Y., Hertman, I. et al. Identification and characterization of the functional α origin of DNA replication of the R6K plasmid and its relatedness to the R6K β and γ origins. Mole Gen Genet 208, 263–270 (1987). https://doi.org/10.1007/BF00330452
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DOI: https://doi.org/10.1007/BF00330452