Koch K S, Gleiberman A S, Aoki T, Leffert H L, Feren A, Jones A L, Fodor E J
Department of Pharmacology, School of Medicine, University of California, San Diego, La Jolla 92036-0636, USA.
Nucleic Acids Res. 1995 Apr 11;23(7):1098-112. doi: 10.1093/nar/23.7.1098.
An unusual S1-nuclease sensitive microsatellite (STMS) has been found in the single copy, rat polymeric immunoglobulin receptor gene (PIGR) terminal exon. In Fisher rats, elements within or beyond the STMS are expressed variably in the 3' untranslated regions (3'UTRs) of two 'Groups' of PIGR-encoded hepatic mRNAs (pIg-R) during liver regeneration. STMS elements include neighboring constant regions (a 60-bp d[GA]-rich tract with a chi-like octamer, followed by 15 tandem d[GGA] repeats) that merge directly with 36 or 39 tandem d[GAA] repeats (Fisher or Wistar strains, respectively) interrupted by d[AA] between their 5th-6th repeat units. The Wistar STMS is flanked upstream by two regions of nearly contiguous d[CA] or d[CT] repeats in the 3' end of intron 8; and downstream, by a 283 bp 'unit' containing several inversions at its 5' end, and two polyadenylation signals at its 3' end. The 283 nt unit is expressed in Group 1 pIg-R mRNAs; but it is absent in the Group 2 family so that their GAA repeats merge with their poly A tails. In contrast to genomic sequence, GGA triplet repeats are amplified (n > or = 24-26), whereas GAA triplet repeats are truncated variably (n < or = 9-37) and expressed uninterruptedly in both mRNA Groups. These results suggest that 3' end processing of the rat PIGR gene may involve misalignment, slippage and premature termination of RNA polymerase II. The function of this unusual processing and possible roles of chi-like octamers in quiescent or extrahepatic tissues are discussed.
在大鼠单拷贝的多聚免疫球蛋白受体基因（PIGR）末端外显子中发现了一种不寻常的对S1核酸酶敏感的微卫星（STMS）。在费希尔大鼠中，STMS内部或外部的元件在肝脏再生过程中，在PIGR编码的肝脏mRNA（pIg-R）的两个“组”的3'非翻译区（3'UTR）中表达存在差异。STMS元件包括相邻的恒定区（一个富含d[GA]的60 bp片段，带有一个类似chi的八聚体，随后是15个串联的d[GGA]重复序列），它们直接与36个或39个串联的d[GAA]重复序列（分别为费希尔或威斯塔大鼠品系）合并，在其第5 - 6个重复单元之间被d[AA]打断。威斯塔大鼠的STMS在8号内含子3'端的上游侧翼是两个几乎连续的d[CA]或d[CT]重复序列区域；在下游，是一个283 bp的“单元”，其5'端包含几个倒位，3'端有两个聚腺苷酸化信号。这个283 nt的单元在第1组pIg-R mRNA中表达；但在第2组家族中不存在，因此它们的GAA重复序列与它们的聚A尾巴合并。与基因组序列不同，GGA三联体重复序列被扩增（n≥24 - 26），而GAA三联体重复序列则被不同程度地截断（n≤9 - 37），并在两个mRNA组中连续表达。这些结果表明，大鼠PIGR基因的3'端加工可能涉及RNA聚合酶II的错配、滑动和过早终止。本文讨论了这种不寻常加工的功能以及类似chi的八聚体在静止或肝外组织中的可能作用。
