Ivessa A S, Zhou J Q, Zakian V A
Department of Molecular Biology, Princeton University, New Jersey 08544-1014, USA.
Cell. 2000 Feb 18;100(4):479-89. doi: 10.1016/s0092-8674(00)80683-2.
Replication of Saccharomyces ribosomal DNA (rDNA) proceeds bidirectionally from origins in a subset of the approximately 150 tandem repeats, but the leftward-moving fork stops when it encounters the replication fork barrier (RFB). The Pif1p helicase and the highly related Rrm3p were rDNA associated in vivo. Both proteins affected rDNA replication but had opposing effects on fork progression. Pif1p helped maintain the RFB. Rrm3p appears to be the replicative helicase for rDNA as it acted catalytically to promote fork progression throughout the rDNA. Loss of Rrm3p increased rDNA breakage and accumulation of rDNA circles, whereas breakage and circles were less common in pif1 cells. These data support a model in which replication fork pausing causes breakage and recombination in the rDNA.
酿酒酵母核糖体DNA（rDNA）在大约150个串联重复序列的一个子集中从起始点双向复制，但向左移动的叉在遇到复制叉屏障（RFB）时会停止。Pif1p解旋酶和高度相关的Rrm3p在体内与rDNA相关联。这两种蛋白质都影响rDNA复制，但对叉的进展有相反的影响。Pif1p有助于维持RFB。Rrm3p似乎是rDNA的复制解旋酶，因为它催化作用以促进整个rDNA中的叉进展。Rrm3p的缺失增加了rDNA断裂和rDNA环的积累，而在pif1细胞中，断裂和环则不太常见。这些数据支持了一个模型，其中复制叉暂停会导致rDNA中的断裂和重组。
