Hausmann S, Jacques J P, Kolakofsky D
Department of Genetics and Microbiology, University of Geneva School of Medicine, Switzerland.
RNA. 1996 Oct;2(10):1033-45.
Paramyxoviruses cotranscriptionally edit their P gene mRNA by the programmed insertion of G residues into a short G run contained within a larger purine run, via pseudo-templated transcription. The templates for paramyxovirus transcription are genome nucleocapsids in which each nucleoprotein subunit is associated with 6 nt, and only genomes whose lengths are multiples of 6 are found naturally or are replicated efficiently in transfected cell systems. We have examined the effect of varying total genome length on the frequency and number of insertions into the mRNA editing site in a transfected cell system, using constructs that generate mini-genome analogues. We found that, as long as the purine run sequence and the region immediately upstream were unaltered, editing occurred during mRNA synthesis independent of the precise length of the minigenome. However, when mini-genome constructs whose lengths were not multiples of 6 were used, insertions (or deletions) occurred during antigenome synthesis within the purine run, which strikingly restored the hexamer length. Genome length correction due to changes in the antigenome purine run length occurred only when the mini-genome was not a multiple of 6, and these changes were only poorly affected by mutations in the mRNA editing site and the region immediately upstream. Our results suggest that the mRNA editing site is a natural hotspot for viral polymerase slippage during genome replication, and that this site serves the dual and complementary function of maintaining hexamer genome length. The unusual requirement of paramyxoviruses for genomes of precise hexamer length may have evolved to maintain genome stability against insertions in the mRNA editing site during replication.
副粘病毒通过假模板转录，在较大嘌呤序列中的短G序列中程序性插入G残基，对其P基因mRNA进行共转录编辑。副粘病毒转录的模板是基因组核衣壳，其中每个核蛋白亚基与6个核苷酸相关联，只有长度为6的倍数的基因组才能在自然条件下被发现，或在转染细胞系统中高效复制。我们使用产生微型基因组类似物的构建体，在转染细胞系统中研究了改变总基因组长度对mRNA编辑位点插入频率和数量的影响。我们发现，只要嘌呤序列和紧邻上游的区域不变，编辑就在mRNA合成过程中发生，与微型基因组的精确长度无关。然而，当使用长度不是6的倍数的微型基因组构建体时，在嘌呤序列中的反基因组合成过程中会发生插入（或缺失），这显著恢复了六聚体长度。只有当微型基因组不是6的倍数时，才会由于反基因组嘌呤序列长度的变化而发生基因组长度校正，并且这些变化仅受mRNA编辑位点和紧邻上游区域突变的轻微影响。我们的结果表明，mRNA编辑位点是基因组复制过程中病毒聚合酶滑动的天然热点，并且该位点具有维持六聚体基因组长度的双重互补功能。副粘病毒对精确六聚体长度基因组的异常要求可能已经进化，以维持基因组在复制过程中对mRNA编辑位点插入的稳定性。
