Abe A, Hiraoka Y, Fukasawa T
Kitasato Institute, Tokyo, Japan.
EMBO J. 1990 Nov;9(11):3691-7. doi: 10.1002/j.1460-2075.1990.tb07581.x.
We have identified a signal sequence (designated core signal) necessary to specify formation of mRNA 3' end of the GAL7 gene in Saccharomyces cerevisiae within a DNA segment 26 bp long. The sequence was located 4-5 nucleotides upstream from the 3' end, i.e. the polyadenylation site, of the GAL7 mRNA. Replacement of a DNA segment encompassing the polyadenylation site with a pBR322 DNA, leaving the core signal intact, resulted in alteration of the mRNA 3' end by several nucleotides, suggesting the existence of an additional signal (designated end signal) at or near the polyadenylation site. The normal end formation was abolished when the core signal was placed in the reverse orientation. A considerable fraction of pre-mRNA synthesized in vitro with SP6 RNA polymerase on the template of a DNA fragment containing these signals was cleaved and polyadenylated presumably at the in vitro 3' end during incubation in a cell-free system of yeast. By contrast pre-mRNA synthesized on the template with the core signal alone was processed but much less efficiently. No such processing was seen when the pre-mRNA either lacked the core signal or contained it in the reverse orientation.
我们已经在一段26bp长的DNA片段中鉴定出了酿酒酵母中指定GAL7基因mRNA 3'端形成所必需的信号序列（称为核心信号）。该序列位于GAL7 mRNA 3'端（即聚腺苷酸化位点）上游4-5个核苷酸处。用pBR322 DNA替换包含聚腺苷酸化位点的DNA片段，同时保持核心信号完整，导致mRNA 3'端改变了几个核苷酸，这表明在聚腺苷酸化位点或其附近存在另一个信号（称为末端信号）。当核心信号以相反方向放置时，正常的末端形成被消除。在含有这些信号的DNA片段模板上，用SP6 RNA聚合酶体外合成的相当一部分前体mRNA在酵母无细胞系统孵育过程中，大概在体外3'端被切割并聚腺苷酸化。相比之下，仅以核心信号为模板合成的前体mRNA也会进行加工，但效率要低得多。当前体mRNA要么缺乏核心信号，要么以相反方向包含该信号时，则看不到这种加工过程。
