Most SINEs consist of two or more modules: 50
-terminal
‘head,’ ‘body’ and 30
-terminal ‘tail.’ The head of all SINE
families known to date demonstrate a clear similarity with one
of the three types of RNA synthesized by pol III: tRNA, 7SL
RNA, or 5S rRNA. The origin of SINE bodies is not easy to
trace, although it has a region descending from one of the
LINEs in a large fraction of SINE families. The tail is a
sequence of variable length consisting of simple (often
degenerate) repeats.