Bhat B M, Wold W S
Institute for Molecular Virology, Saint Louis University School of Medicine, Missouri 63100.
J Virol. 1987 Dec;61(12):3938-45. doi: 10.1128/JVI.61.12.3938-3945.1987.
The E3 complex transcription unit of adenovirus encodes overlapping mRNAs (a to i) with different exon structures. The major mRNAs are a (approximately 40% of the total) and c (approximately 15%), which are spliced once, and f (approximately 15%) and h (approximately 25%), which are spliced twice. mRNA a uses the upstream E3A polyadenylation site, and the other mRNAs use the downstream E3B polyadenylation site. We analyzed virus deletion mutants to identify sequences important in alternative pre-mRNA processing in region E3. Our main finding is that a 64-base-pair deletion in dl742 causes mainly mRNAs f and h to be formed. mRNAs a and c are barely made. dl742 does not delete either a splice site or a polyadenylation site. Thus, the sequences deleted must function in alternative pre-mRNA processing independently of the signals at the actual splice and polyadenylation sites. The lack of synthesis of mRNA a by dl742 does not appear to result from a defect in the E3A polyadenylation signal but rather from an increase in splicing activity which results in the synthesis of doubly spliced mRNAs f and h at the expense of singly spliced mRNAs a and c. This suggests, in the wild-type situation, that the frequency of use of the E3A versus the E3B polyadenylation site may be determined by the rate of splicing, as well as, presumably, the rate of cleavage-polyadenylation at the E3A site.
腺病毒的E3复合转录单元编码具有不同外显子结构的重叠mRNA（a至i）。主要的mRNA是a（约占总量的40%）和c（约15%），它们进行一次剪接；f（约15%）和h（约25%），它们进行两次剪接。mRNA a使用上游的E3A聚腺苷酸化位点，其他mRNA使用下游的E3B聚腺苷酸化位点。我们分析了病毒缺失突变体，以确定E3区域中前体mRNA可变加工过程中重要的序列。我们的主要发现是，dl742中64个碱基对的缺失主要导致mRNA f和h的形成。mRNA a和c几乎不产生。dl742既没有删除剪接位点也没有删除聚腺苷酸化位点。因此，缺失的序列必须在不依赖于实际剪接和聚腺苷酸化位点信号的前体mRNA可变加工中发挥作用。dl742导致mRNA a缺乏合成，这似乎不是由于E3A聚腺苷酸化信号缺陷，而是由于剪接活性增加，导致以单剪接的mRNA a和c为代价合成双剪接的mRNA f和h。这表明，在野生型情况下，E3A与E3B聚腺苷酸化位点的使用频率可能由剪接速率以及推测的E3A位点的切割-聚腺苷酸化速率决定。
