The Echo™ Cloning System is a two-vector system that utilizes the Cre-lox site-specific recombination system of bacteriophage P1 (1,2) for rapid cloning into multiple vectors. Your gene of interest is cloned into one of the specially designed donor vectors which can then be recombined with as many different Echo™ acceptor vectors as desired. The donor and acceptor vectors are placed in a buffer that contains Cre recombinase for a 25-minute, in vitro recombination reaction. Cre binds to the lox site present on each vector, brings them together, then cleaves and covalently reattaches the DNA strands. The end result is a fusion of the donor and acceptor vectors forming a single, functional expression vector.
PIR1 competent cells are for cloning and maintenance of your donor vector (i.e. pUniV5/His-TOPO™) construct (or other vector containing the R6K-gamma origin). It contains a mutant allele of the pir gene that maintains the donor vector construct at ∼250 copies per cell.