Abstract
Various studies suggest that eukaryotic chromosomes may occupy
distinct territories within the nucleus and that chromosomes are
tethered to a nuclear matrix. These constraints might limit
interchromosomal interactions. We have used a molecular genetic test to
investigate whether the chromosomes of
Saccharomyces
cerevisiae
exhibit such territoriality. A chromosomal
double-strand break (DSB) can be efficiently repaired by recombination
between flanking homologous repeated sequences. We have constructed a
strain in which DSBs are delivered simultaneously to both chromosome
III and chromosome V by induction of the HO endonuclease. The
arrangement of partially duplicated
HIS4
and
URA3
sequences around each HO recognition site allows
the repair of the two DSBs in two alternative ways: (
i
)
the creation of two intrachromosomal deletions or (
ii
)
the formation of a pair of reciprocal translocations. We show that
reciprocal translocations are formed approximately as often as the pair
of intrachromosomal deletions. Similar results were obtained when one
of the target regions was moved from chromosome V to any of three
different locations on chromosome XI. These results argue that the
broken ends of mitotic chromosomes are free to search the entire genome
for appropriate partners; thus, mitotic chromosomes are not
functionally confined to isolated domains of the nucleus, at least when
chromosomes are broken.