Hogan N C, Slot F, Traverse K L, Garbe J C, Bendena W G, Pardue M L
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
Genetics. 1995 Apr;139(4):1611-21. doi: 10.1093/genetics/139.4.1611.
The Drosophila melanogaster Hsr-omega locus produces a nuclear RNA containing > 5 kb of tandem repeat sequences. These repeats are unique to Hsr-omega and show concerted evolution similar to that seen with classical satellite DNAs. In D. melanogaster the monomer is approximately 280 bp. Sequences of 19 1/2 monomers differ by 8 +/- 5% (mean +/- SD), when all pairwise comparisons are considered. Differences are single nucleotide substitutions and 1-3 nucleotide deletions/insertions. Changes appear to be randomly distributed over the repeat unit. Outer repeats do not show the decrease in monomer homogeneity that might be expected if homogeneity is maintained by recombination. However, just outside the last complete repeat at each end, there are a few fragments of sequence similar to the monomer. The sequences in these flanking regions are not those predicted for sequences decaying in the absence of recombination. Instead, the fragmentation of the sequence homology suggests that flanking regions have undergone more severe disruptions, possibly during an insertion or amplification event. Hsr-omega alleles differing in the number of repeats are detected and appear to be stable over a few thousand generations; however, both increases and decreases in repeat numbers have been observed. The new alleles appear to be as stable as their predecessors. No alleles of less than approximately 5 kb nor more than approximately 16 kb of repeats were seen in any stocks examined. The evidence that there is a limit on the minimum number of repeats is consistent with the suggestion that these repeats are important in the function of the unusual Hsr-omega nuclear RNA.
果蝇的Hsr-omega基因座产生一种核RNA，其包含超过5 kb的串联重复序列。这些重复序列是Hsr-omega所特有的，并且显示出与经典卫星DNA相似的协同进化。在黑腹果蝇中，单体约为280 bp。当考虑所有成对比较时，19.5个单体的序列差异为8±5%（平均值±标准差）。差异为单核苷酸取代以及1 - 3个核苷酸的缺失/插入。变化似乎随机分布在重复单元上。外部重复序列并未显示出如果通过重组维持同质性可能预期的单体同质性降低。然而，在每一端最后一个完整重复序列之外，有一些与单体相似的序列片段。这些侧翼区域中的序列并非在无重组情况下序列衰减所预测的那些序列。相反，序列同源性的片段化表明侧翼区域经历了更严重的破坏，可能是在插入或扩增事件期间。检测到重复次数不同的Hsr-omega等位基因，并且在几千代中似乎是稳定的；然而，已经观察到重复次数的增加和减少。新的等位基因似乎与其前身一样稳定。在任何检测的品系中都未见到重复序列少于约5 kb或多于约16 kb的等位基因。存在重复序列最小数量限制的证据与这些重复序列在异常的Hsr-omega核RNA功能中很重要的观点一致。
