Qiu Jianming, Pintel David J
Department of Molecular Microbiology and Immunology, University of Missouri, School of Medicine, Columbia, Missouri 65212, USA.
J Biol Chem. 2004 Apr 9;279(15):14889-98. doi: 10.1074/jbc.M312734200. Epub 2004 Jan 27.
Adeno-associated virus type 5 is unique among adeno-associated virus serotypes in that it uses a polyadenylation site in the center of the genome. The great majority of transcripts generated from the upstream P7 and P19 promoters are polyadenylated at a site in the central intron ((pA)p); however, most of the viral transcripts generated by the proximal P41 promoter are polyadenylated at the distal polyadenylation site at the 3' end of the genome (pA)d and subsequently spliced. Polyadenylation at (pA)p increases as the distance between the RNA initiation site and the intron and (pA)p site is increased. The steady-state level of RNAs polyadenylated at (pA)p is independent of the promoter used or of the intervening sequence but is dependent upon competition with splicing, inhibition by U1 snRNP binding to the intron donor, and the intrinsic efficiency of the cleavage/polyadenylation reaction. Each of these determinants shows a marked dependence on the distance between the RNA initiation site and the intron and (pA)p. Finally, unlike other reported systems, inhibition of (pA)p by U1 snRNP binding to the intron donor is decreased as the distance between the donor and (pA)p is increased.
5型腺相关病毒在腺相关病毒血清型中独具特色，因为它在基因组中心使用一个聚腺苷酸化位点。从上游P7和P19启动子产生的绝大多数转录本在中央内含子中的一个位点（(pA)p）进行聚腺苷酸化；然而，由近端P41启动子产生的大多数病毒转录本在基因组3'端的远端聚腺苷酸化位点（(pA)d）进行聚腺苷酸化，随后进行剪接。随着RNA起始位点与内含子及(pA)p位点之间距离的增加，(pA)p处的聚腺苷酸化作用增强。在(pA)p处进行聚腺苷酸化的RNA的稳态水平与所使用的启动子或中间序列无关，但取决于与剪接的竞争、U1 snRNP与内含子供体结合的抑制作用以及切割/聚腺苷酸化反应的内在效率。这些决定因素中的每一个都显著依赖于RNA起始位点与内含子及(pA)p之间的距离。最后，与其他报道系统不同的是，随着供体与(pA)p之间距离的增加，U1 snRNP与内含子供体结合对(pA)p的抑制作用减弱。
