Abstract
Chromatin assembly factor-1 (CAF-1) is involved in nucleosome assembly following DNA replication and nucleotide excision repair. In Arabidopsis thaliana, the 3 CAF-1 subunits p150, p60 and p48 are encoded by FAS1, FAS2 and MSI1, respectively. Since nucleosome assembly is expected to be reduced or delayed in mutants lacking CAF-1 activity, we asked whether genomic stability is altered in fas1 and fas2 mutants. Depletion of either subunit enhanced the frequency of somatic homologous recombination (HR) in planta 40-fold. The frequency of T-DNA integration was also elevated. A delay in loading histones onto newly replicated or repaired DNA might make these DNA stretches more accessible, both to repair enzymes and to foreign DNA. Furthermore, fas mutants exhibited increased levels of DNA double-strand breaks, a prolonged S-phase, and elevated levels of mRNAs coding for proteins involved in HR. Also these factors could contribute to up-regulation of HR frequency in fas mutants.
