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Recombinase Enhancer 
R.C. Johnson and M.F. Bruist. 1989. Intermediates in Hin-mediated DNA inversion: a role for Fis and the recombinational enhancer in the strand exchange reaction
[http://www.pubmedcentral.gov/picrender.fcgi?tool=pmcentrez&blobtype=pdf&artid=400990]
#RE sequence must be present
#w/o RE, Hin can still assemble to with the two Hix’s however, Hin can’t generate inversion
#Prevention of Fis binding causes loss of enhancer function
#60 bp in length
#Binds two Fis proteins (98 AA’s)
#Enhancer cannot function when located too close to a recombination site
#HU facilitates the required bending of the DNA to create the inversion interaction
#HU stimulation is dependent upon location of RE
#Dependence upon HU is lesser when distance between RE and recombination site is greater
#Required to induce the bending of the shorter, yet stiffer, segment of DNA 
#When RE is located >650 bp for the recombination site the dependence upon HU to form the complex is lost
#RE combined w/ supercoiling mediate the rotation of DNA strands subsequent to double-stranded cleavage by Hin within two recombination sites

Haykinson and Johnson. 1993. DNA looping and the helical repeat in vitro and in vivo: effect of HU protein and enhancer location on Hin invertasome assembly
[http://www.pubmedcentral.gov/articlerender.fcgi?tool=pubmed&pubmedid=8508775]
#The two recombination sites bound by Hin are assembled together at the Fis-bound RE
#w/o HU invertasome assembly is very inefficient
#“HU is the only protein in E. coli that can promote invertasome formation with short DNA lengths between RE and recombination sites
#HU binds non-specifically to DNA between the enhancer and recombination site to facilitate DNA looping
#“The RE can function at great distances !!! >4 kb !!! and on either side of a recombination site on a plasmid to stimulate Hin-mediated DNA inversion”
#RE is not functional at a position 32 bp minimum
#Due to restricted looping
#Enhancer Structure: AGTCAACAATTGACC – 33 bp – GTGCAAATTGTGACC; proximal Fis-binding site of the left and the distal Fis-binding site on the right