Johnson R E, Kovvali G K, Prakash L, Prakash S
Sealy Center for Molecular Science, University of Texas Medical Branch, 6.104 Medical Research Building, Galveston, TX 77555-1061, USA.
Curr Genet. 1998 Jul;34(1):21-9. doi: 10.1007/s002940050362.
The RTH1(RAD27) gene of Saccharomyces cerevisiae encodes a structure-specific endonuclease that cleaves 5'-ended single-stranded DNA at its junction with duplex DNA. Genetic and biochemical studies have indicated a role of Rth1 nuclease in the removal of RNA primers formed during DNA replication. The rth1Delta mutation confers temperature-sensitive lethality, and increases sensitivity to alkylating agents. The instability of repetitive DNA is greatly enhanced in the rth1Delta mutant. The conditional lethality of the rth1Delta mutation indicates that another nuclease can function in DNA replication in the absence of RTH1. RAD2, a homolog of RTH1, is required for nucleotide-excision repair. Here, we examine three other homologs of RTH1/RAD2 - YEN1, EXO1, and DIN7. Deletion of any of these genes in the rth1Delta strain has no effect on cell viability, suggesting the involvement of another, and as yet unidentified, nuclease in the maturation of Okazaki fragments. Our data also indicate that only RTH1 functions in the repair of alkylation damage. Deletions of YEN1, EXO1, DIN7, or RAD2, either singly or when combined with one another and with the rth1Delta mutation, have no effect on the rate of instability of dinucleotide repeats or on the rate of formation of large duplications in the CAN1 gene. These data provide evidence of a high degree of specificity for the role of RTH1 in DNA replication and in base-excision repair, and for the requirement of RAD2 in nucleotide-excision repair. The possibility that both Rth1 and Exo1 function in DNA mismatch repair is discussed.
酿酒酵母的RTH1（RAD27）基因编码一种结构特异性核酸内切酶，该酶可在5'端单链DNA与双链DNA的连接处切割。遗传和生化研究表明，Rth1核酸酶在去除DNA复制过程中形成的RNA引物方面发挥作用。rth1Δ突变导致温度敏感型致死，并增加对烷化剂的敏感性。在rth1Δ突变体中，重复DNA的不稳定性大大增强。rth1Δ突变的条件致死性表明，在没有RTH1的情况下，另一种核酸酶可以在DNA复制中发挥作用。RAD2是RTH1的同源物，是核苷酸切除修复所必需的。在这里，我们研究了RTH1/RAD2的其他三个同源物——YEN1、EXO1和DIN7。在rth1Δ菌株中删除这些基因中的任何一个对细胞活力都没有影响，这表明另一种尚未确定的核酸酶参与了冈崎片段的成熟。我们的数据还表明，只有RTH1在烷基化损伤修复中起作用。单独或相互组合以及与rth1Δ突变一起删除YEN1、EXO1、DIN7或RAD2，对二核苷酸重复序列的不稳定性速率或CAN1基因中大型重复序列的形成速率没有影响。这些数据为RTH1在DNA复制和碱基切除修复中的作用以及RAD2在核苷酸切除修复中的需求提供了高度特异性的证据。还讨论了Rth1和Exo1在DNA错配修复中发挥作用的可能性。
