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.
Sequence variation of Ribosomal DNA Internal Transcribed Spacer 1 of Hyriopsis cumingii from the Five Freshwater Lakes of China
