 Upon encountering a Chi site , the activity of the RecBCD enzyme changes drastically . DNA unwinding pauses for a few seconds and then resumes at roughly half the initial speed . This is likely because the slower RecB helicase unwinds the DNA after Chi , rather than the faster RecD helicase , which unwinds the DNA before Chi . Recognition of the Chi site also changes the RecBCD enzyme so that it cuts the DNA strand with Chi and begins loading multiple RecA proteins onto the single @-@ stranded DNA with the newly generated 3 ' end . The resulting RecA @-@ coated nucleoprotein filament then searches out similar sequences of DNA on a homologous chromosome . The search process induces stretching of the DNA duplex , which enhances homology recognition ( a mechanism termed conformational proofreading ) . Upon finding such a sequence , the single @-@ stranded nucleoprotein filament moves into the homologous recipient DNA duplex in a process called strand invasion . The invading 3 ' overhang causes one of the strands of the recipient DNA duplex to be displaced , to form a D @-@ loop . If the D @-@ loop is cut , another swapping of strands forms a cross @-@ shaped structure called a Holliday junction . Resolution of the Holliday junction by some combination of RuvABC or RecG can produce two recombinant DNA molecules with reciprocal genetic types , if the two interacting DNA molecules differ genetically . Alternatively , the invading 3 ’ end near Chi can prime DNA synthesis and form a replication fork . This type of resolution produces only one type of recombinant ( non @-@ reciprocal ) . 
