Cassidy J R, Pukkila P J
Department of Biology, University of North Carolina, Chapel Hill 27514.
Curr Genet. 1987;12(1):33-6. doi: 10.1007/BF00420724.
In the basidiomycete fungus Coprinus cinereus, the 5S ribosomal RNA (rRNA) genes are found in the rDNA repeat which encodes the other three rRNAs (18S, 5.8S, and 26S), and all genes are transcribed in the same direction (Cassidy et al. 1984). To facilitate examination of the rRNA gene organization in additional species, we developed a method to permit determination of the direction of transcription of the rRNA genes using crude preparations of genomic DNA. We used this method to determine the organization of the rDNA in five other members of the order Agaricales (Flammulina velutipes, Agaricus bisporus, Coprinus micaceus, Coprinus atramentarius, and Coprinus comatus). In four, the organization is the same as it is in Coprinus cinereus. However, in Coprinus comatus, the 5S RNA gene is present in the rDNA repeat, but is transcribed in the opposite direction. This alteration in rDNA organization within the genus Coprinus indicates that inverted 5S genes can arise and become propagated through the tandem array of genes. The presence of orientation-dependent promoter elements within the spacer DNA (Elion and Warner 1984) would be expected to place constraints on such inversions.
在担子菌纲真菌灰盖鬼伞中，5S核糖体RNA（rRNA）基因存在于编码其他三种rRNA（18S、5.8S和26S）的rDNA重复序列中，并且所有基因都沿相同方向转录（卡西迪等人，1984年）。为了便于研究其他物种中的rRNA基因组织，我们开发了一种方法，可利用基因组DNA的粗提物来确定rRNA基因的转录方向。我们用这种方法确定了伞菌目其他五个成员（金针菇、双孢蘑菇、云母鬼伞、墨汁鬼伞和毛头鬼伞）中rDNA的组织情况。在其中四个物种中，其组织情况与灰盖鬼伞相同。然而，在毛头鬼伞中，5S RNA基因存在于rDNA重复序列中，但转录方向相反。鬼伞属内rDNA组织的这种变化表明，反向的5S基因能够出现并通过基因串联阵列进行传播。间隔DNA中存在方向依赖性启动子元件（埃利昂和华纳，1984年），预计会对这种倒位产生限制。
