Mapping and Characterization of a Rac DNA Fragment that Permits Lytic Growth of λ red, gam on recA Hosts.

Abstract

A Fec⁺ λ clone, λdL11*4.8, contains a 2.5 kb insert of E. coli Rac prophage DNA. It is not recE nor is it λ rev. A series of nested deletions for the Fec⁺ phenotype was prepared and the activity was mapped to a sequence that is between 300 bp and 900 bp long. Coinfection experiments confirm earlier findings that the insert acts in a CIS manner. Plasmids carrying the active Rac fragment exhibit fragment orientation-dependent forms upon agarose gel electrophoresis. Two models were tested to account for the fragments phenotype. Model one was that the insert was providing a sequence for site specific recombination. An alternative model is that the insert is providing a RecBCD insensitive origin of phage replication. A system to measure recombination of insert containing plasmid in various host backgrounds produced results with he expected Rac-dependent, A-independent plasmid multimerization to support the hypothesis for site specific recombination. The insert did not support the replication of a chloramphenicol resistance cassette. This result is not consistent with the hypothesis that the insert is an alternative origin of replication. If the insert is an origin of replication then it must require another element in order to elicit its Fec⁺ phenotype.