Byrne Deborah, Grzela Renata, Lartigue Audrey, Audic Stéphane, Chenivesse Sabine, Encinas Stéphanie, Claverie Jean-Michel, Abergel Chantal
Structural and Genomic Information Laboratory, CNRS-UPR 2589, IFR-88, Aix-Marseille University, Parc Scientifique de Luminy, Case 934, 13288 Marseille Cedex 9, France.
Genome Res. 2009 Jul;19(7):1233-42. doi: 10.1101/gr.091561.109. Epub 2009 Apr 29.
Mimivirus, a giant DNA virus infecting Acanthamoeba, is revealing an increasing list of unique features such as a 1.2-Mb genome with numerous genes not found in other viruses, a uniquely conserved promoter signal, and a particle of unmatched complexity using two distinct portals for genome delivery and packaging. Herein, we contribute a further Mimivirus distinctive feature discovered by sequencing a panel of viral cDNAs produced for probing the structure of Mimivirus transcripts. All Mimivirus mRNAs are polyadenylated at a site coinciding exactly with unrelated, but strongly palindromic, genomic sequences. The analysis of 454 Life Sciences (Roche) FLX cDNA tags (150,651) confirmed this finding for all Mimivirus genes independent of their transcription timings and expression levels. The absence of a suitable palindromic signal between adjacent genes results in transcripts encompassing multiple ORFs in the same or even in opposite orientations. Surprisingly, Mimivirus tRNAs are expressed as polyadenylated messengers, including an ORF/tRNA composite mRNA. To our knowledge, both the nature and the stringency of the "hairpin rule" defining the location of polyadenylation sites are unique, raising once more the question of Mimivirus's evolutionary origin. The precise molecular mechanisms implementing the hairpin rule into the 3'-end processing of Mimivirus pre-mRNAs remain to be elucidated.
米米病毒是一种感染棘阿米巴原虫的巨型DNA病毒，它展现出越来越多独特的特征，比如拥有一个120万个碱基对的基因组，其中有许多基因在其他病毒中未被发现；有一个独特保守的启动子信号；还有一个结构极其复杂的病毒颗粒，其基因组的传递和包装使用两个不同的通道。在此，我们通过对一组为探究米米病毒转录本结构而产生的病毒cDNA进行测序，又发现了米米病毒的一个独特特征。所有米米病毒的mRNA在一个位点进行多聚腺苷酸化，该位点恰好与不相关但具有强烈回文结构的基因组序列重合。对454生命科学公司（罗氏）的FLX cDNA标签（150,651个）进行分析，证实了所有米米病毒基因都存在这一现象，与它们的转录时间和表达水平无关。相邻基因之间缺乏合适的回文信号，导致转录本包含同一方向甚至相反方向的多个开放阅读框。令人惊讶的是，米米病毒的tRNA以多聚腺苷酸化信使的形式表达，包括一个开放阅读框/tRNA复合mRNA。据我们所知，定义多聚腺苷酸化位点位置的“发夹规则”的性质和严格性都是独一无二的，这再次引发了米米病毒进化起源的问题。将发夹规则应用于米米病毒前体mRNA 3'端加工的精确分子机制仍有待阐明。
