Complex sentence: At the end of the Soviet era, GUM was partially then fully privatized, and it passed through a number of owners before it ended up in the hands of the supermarket chain Perekryostok.
Split into simpler sentences: At the end of the Soviet era, GUM was partially--and then fully--privatized, and passed through a number of owners. It ended up in the hands of the supermarket chain Perekryostok.