Hug M, Hotz H R, Hartmann C, Clayton C
Zentrum für Molekulare Biologie, Heidelberg, Federal Republic of Germany.
Mol Cell Biol. 1994 Nov;14(11):7428-35. doi: 10.1128/mcb.14.11.7428-7435.1994.
Nearly all trypanosome mRNAs are synthesized as polycistronic precursors, from which mature mRNAs are excised by trans splicing and polyadenylation. Polyadenylation of a procyclic acidic repetitive protein (PARP, or procyclin) transcript was studied by transient transfection of constructs bearing a chloramphenicol acetyltransferase gene linked to the PARP intergenic region. Polyadenylation usually occurred at A residues, about 100 bases upstream of a trans-splicing acceptor signal. The wild-type polyadenylation site has a cryptic trans-splicing signal about 100 bp downstream: deletion or inversion of this signal results in polyadenylation at multiple sites, upstream of other cryptic trans-splicing signals. The PARP mRNA precursor appears to contain a hierarchy of possible processing signals, the function of cryptic ones being revealed only when the dominant ones are deleted or moved. Correct polyadenylation can be restored by addition of trans-splicing signals from other loci. The results indicate that polyadenylation is coupled to downstream trans splicing but that the products of the trans-splicing reaction are not necessarily functional mRNAs.
几乎所有锥虫的信使核糖核酸（mRNA）都是作为多顺反子前体合成的，成熟的mRNA通过反式剪接和聚腺苷酸化从这些前体中切除。通过瞬时转染携带与锥虫酸性重复蛋白（PARP，即前环素）基因间隔区相连的氯霉素乙酰转移酶基因的构建体，对前环素转录本的聚腺苷酸化进行了研究。聚腺苷酸化通常发生在反式剪接受体信号上游约100个碱基处的A残基上。野生型聚腺苷酸化位点在下游约100 bp处有一个隐蔽的反式剪接信号：该信号的缺失或倒置会导致在其他隐蔽反式剪接信号上游的多个位点发生聚腺苷酸化。PARP mRNA前体似乎包含一系列可能的加工信号，只有当显性信号被删除或移动时，隐蔽信号的功能才会显现出来。通过添加来自其他位点的反式剪接信号可以恢复正确的聚腺苷酸化。结果表明，聚腺苷酸化与下游反式剪接相关联，但反式剪接反应的产物不一定是功能性mRNA。
