Winston F, Dollard C, Malone E A, Clare J, Kapakos J G, Farabaugh P, Minehart P L
Genetics. 1987 Apr;115(4):649-56. doi: 10.1093/genetics/115.4.649.
Mutations in the SPT3 gene were isolated as one class of suppressors of Ty and solo delta insertion mutations in Saccharomyces cerevisiae. Previous work has shown that null mutations in SPT3 abolish the normal Ty delta-delta transcript; instead, a transcript that initiates 800 bases farther downstream is made, suggesting that SPT3 is required for transcription initiation in delta sequences. We have selected for new spt mutations and have screened for those with the unique suppression pattern of spt3 mutations with respect to two insertion mutations. Our selection and screen has identified two additional genes, SPT7 and SPT8, that are also required for transcription initiation in delta sequences. We show that mutations in SPT7 or SPT8 result in the same alteration of Ty transcription as do mutations in SPT3. In addition, mutations in all three genes cause a sporulation defect. By assay of a Ty-lacZ fusion we have shown that spt3, spt7 and spt8 mutations reduce transcription from a delta sequence by 10-25-fold. Finally, we show that SPT3 mRNA levels are unaffected in either spt7 or spt8 mutants, suggesting that these two genes do not regulate transcription of SPT3.
SPT3基因的突变作为酿酒酵母中Ty和单个δ插入突变的一类抑制子被分离出来。先前的研究表明，SPT3基因的无效突变会消除正常的Tyδ-δ转录本；相反，会产生一种在下游800个碱基处起始的转录本，这表明SPT3是δ序列中转录起始所必需的。我们筛选了新的spt突变，并针对两个插入突变筛选出具有spt3突变独特抑制模式的突变。我们的筛选确定了另外两个基因，SPT7和SPT8，它们也是δ序列中转录起始所必需的。我们发现，SPT7或SPT8基因的突变导致的Ty转录改变与SPT3基因的突变相同。此外，这三个基因的突变都会导致孢子形成缺陷。通过对Ty-lacZ融合体的检测，我们发现spt3、spt7和spt8突变会使δ序列的转录减少10至25倍。最后，我们发现spt7或spt8突变体中的SPT3 mRNA水平不受影响，这表明这两个基因不调节SPT3的转录。
