A student wants to set up a co-immunoprecipitation (co-IP) exeriment and follows this protocol: a. Incubate cells with a cell-permeable reducible crosslinker b. Lyses cells in SDS containing buffer c. Adds DTT to the lysate d. Renatures lysate (adds 10-fold excess of mild detergent) followed by IP with antibodies against 1st protein and then washes with PBS e. Adds DTT to the samples f. Adds SDS containing sample buffer and boils them for 5 min. g. Runs SDS-PAGE followed by immunoblotting with antibodies againt 2nd protein He tests this protocol on two proteins that are known to interact and does not obtain a positive result of co-IP. What step in the protocol is *WRONG*???