We previously identified novel human ets-1 transcripts in which the normal order 
of exons is inverted, and demonstrated that although the order of exons is 
different than in the genomic DNA, splicing of these exons out of order occurs 
in pairs using genuine splice sites (1). Here we determine the structure of 
these novel transcripts, showing that they correspond to circular RNA molecules 
containing only exons in genomic order. These transcripts are stable molecules, 
localized in the cytoplasmic component of the cells. To our knowledge, this is 
the first case of circular transcripts being processed from nuclear pre-mRNA in 
eukaryotes. This new type of transcript might represent a novel aspect of gene 
expression and hold some interesting clues about the splicing mechanism.