Berger S L, Meselson M
Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, MA 02138.
Nucleic Acids Res. 1994 Aug 11;22(15):3218-25. doi: 10.1093/nar/22.15.3218.
Transcription downstream of the polyadenylation site was studied in the Drosophila hsp70 gene, whose high level of transcription in response to temperature elevation facilitates detection of rare and possibly short-lived transcripts. Transcription downstream of the polyadenylation site was detected both in cultured cells and in intact animals. Even shortly after temperature elevation the extended nonpolyadenylated RNAs were rare relative to mature message, and their level continued to increase following temperature elevation even after the amount of mature message stopped increasing. The extended transcripts therefore are unlikely to be message precursors. Although continuous transcripts were detected extending as far as 2 kb downstream of the normal polyadenylation site, the predominant extended transcript was 0.45 kb long, apparently produced by cleavage of longer transcripts. Its amount relative to mature message increased with the duration and severity of heat-shock. As is the case in nonpolyadenylated histone mRNA, there is a potential stem-loop structure just upstream of the cleavage site. These data and other lines of evidence suggest that this extended transcript results from an alternative mode of stable 3'-end formation.
在果蝇hsp70基因中研究了聚腺苷酸化位点下游的转录情况，该基因在温度升高时的高转录水平有助于检测罕见且可能寿命短暂的转录本。在培养细胞和完整动物中均检测到了聚腺苷酸化位点下游的转录。即使在温度升高后不久，相对于成熟的信使RNA，延长的非聚腺苷酸化RNA也很罕见，并且即使在成熟信使RNA的量停止增加后，其水平在温度升高后仍继续上升。因此，延长的转录本不太可能是信使RNA的前体。尽管检测到连续的转录本延伸至正常聚腺苷酸化位点下游2 kb处，但主要的延长转录本长度为0.45 kb，显然是由较长转录本的切割产生的。其相对于成熟信使RNA的量随热休克的持续时间和严重程度而增加。与非聚腺苷酸化组蛋白mRNA的情况一样，在切割位点上游刚好有一个潜在的茎环结构。这些数据和其他证据表明，这种延长的转录本是由稳定的3'末端形成的替代模式产生的。
