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Molecular and Cellular Biology, September 2003, p. 6363-6372, Vol. 23, No. 18
0270-7306/03/$08.00+0 DOI: 10.1128/MCB.23.18.6363-6372.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Primo Schär,2 and Jose M. Sogo1*
Institute of Cell Biology, Swiss Federal Institute of Technology, CH-8093 Zürich,1 Institute of Molecular Cancer Research, CH-8008 Zürich, Switzerland2
Received 3 February 2003/ Returned for modification 2 April 2003/ Accepted 20 June 2003
We investigated the formation of X-shaped molecules consisting of joint circular minichromosomes (joint molecules) in Saccharomyces cerevisiae by two-dimensional neutral/neutral gel electrophoresis of psoralen-cross-linked DNA. The appearance of joint molecules was found to be replication dependent. The joint molecules had physical properties reminiscent of Holliday junctions or hemicatenanes, as monitored by strand displacement, branch migration, and nuclease digestion. Physical linkage of the joint molecules was detected along the entire length of the minichromosome and most likely involved newly replicated sister chromatids. Surprisingly, the formation of joint molecules was found to be independent of Rad52p as well as of other factors associated with a function in homologous recombination or in the resolution of stalled replication intermediates. These findings thus imply the existence of a nonrecombinational pathway(s) for the formation of joint molecules during the process of DNA replication or minichromosome segregation.
Present address: Departemento de Genetica, Universidad de Sevilla, Seville, Spain.
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