van Herwerden L, Blair D, Agatsuma T
Zoology Department, James Cook University, Townsville, Queensland, Australia.
Parasitology. 1998 Apr;116 ( Pt 4):311-7. doi: 10.1017/s003118209800242x.
The first internal transcribed spacer (ITS1) of the nuclear ribosomal DNA repeat was sequenced for members of the Schistosoma japonicum species complex (S. malayensis, S. mekongi and 2 geographical isolates of S. japonicum). The ITS1 is composed of 3 distinct regions: the 5' end (23 nucleotides); a tract of approximately 90-140 nucleotides, which occurs up to 7 times in tandem, the number varying even within an individual in all species investigated in this study; the 3' region (378 nucleotides), which lacks repeats. There is size and sequence variation among copies of the ITS1 repeat within a single individual. The relative abundances of size variants of ITS1 in S. japonicum have been ascertained by hybridizing genomic digests with an ITS1 probe. Multiple repeats and intra-individual variation in numbers and abundance of these is a feature of the Asian schistosomes, but not generally of African schistosomes. Possible reasons for this difference in ITS1 between African and Asian schistosomes are discussed. The ITS1 repeat sequences described for African schistosomes are different to, and cannot be aligned with, those from the Asian species described here, whereas the remainder of the ITS1 can be aligned quite easily.
对日本血吸虫复合种（马来血吸虫、湄公血吸虫以及日本血吸虫的2个地理分离株）的成员，测定了核糖体DNA重复序列的第一个内部转录间隔区（ITS1）。ITS1由3个不同区域组成：5'端（23个核苷酸）；一段约90 - 140个核苷酸的序列，该序列串联出现多达7次，在本研究调查的所有物种中，即使在个体内部其数量也有所不同；3'区域（378个核苷酸），该区域无重复序列。单个个体内ITS1重复序列的拷贝之间存在大小和序列变异。通过用ITS1探针与基因组消化产物杂交，已确定日本血吸虫中ITS1大小变异体的相对丰度。多个重复序列以及这些重复序列在数量和丰度上的个体内变异是亚洲血吸虫的一个特征，但非洲血吸虫通常没有此特征。讨论了非洲和亚洲血吸虫ITS1存在这种差异的可能原因。这里描述的非洲血吸虫的ITS1重复序列与这里描述的亚洲血吸虫的不同，无法进行比对，而ITS1的其余部分则很容易比对。
