Tr. Ward et al., Ribosomal DNA replication fork barrier and HOT1 recombination hot spot: Shared sequences but independent activities, MOL CELL B, 20(13), 2000, pp. 4948-4957
In the ribosomal DNA of Saccharomyces cerevisiae, sequences in the nontrans
cribed spacer 3' of the 35S ribosomal RNA gene are important to the polar a
rrest of replication forks at a site called the replication fork barrier (R
FB) and also to the cis-acting, mitotic hyperrecombination site called HOT1
. We have found that the RFB and HOT1 activity share some but not all of th
eir essential sequences. Many of the mutations that reduce HOT1 recombinati
on also decrease or eliminate fork arrest at one of two closely spaced RFB
sites, RFB1 and RFB2. A simple model for the juxtaposition of RFB and HOT1
sequences is that the breakage of strands in replication forks arrested at
RFB stimulates recombination. Contrary to this model, we show here that HOT
1-stimulated recombination does not require the arrest of forks at the RFB.
Therefore, while HOT1 activity is independent of replication fork arrest,
HOT1 and RFB require some common sequences, suggesting the existence of a c
ommon trans-acting factor(s).