Functional analysis of the replicator structure of lambdoid bacteriophage DNAs

In our hybrid-plasmid reconstruction analysis of lambda (lambdoid) DNA signal structures involved in phage DNA replication, we have detected a dual system alternatingly able to initiate a first primer-RNA synthesis. Both of them--the major, primase-dependent ori system and the minor and usually suppressed, RNA-polymerase-dependent oop system--act in conjunction with a common signal structure for inception of DNA synthesis. It appears that in situations such as this, where one has to deal with the existence of regular as well as backup systems serving the same function, straightforward conclusions are no longer possible in their genetic analysis. For example, even though the oop-DNA segment can be deleted entirely from bacteriophage lambda DNA without disturbing its ability to replicate, it may not be valid to conclude that the oop system has no function in DNA replication. Dual systems of this type or organization in general have also been observed previously for some other replicons such as the R-factors R6-5 and R6K (Timmis et al. 1978; Crosa et al., this volume) or the F factor (Helinski et al., this volume), and they may be more common than presently expected.