Sry is expressed at higher levels in the adult testis, where no function has 
been determined, than in the genital ridge, its critical site of action. cDNA 
and 5' RACE clones isolated from testis or from Sry-transfected cell lines have 
an unusual structure, with 3' sequences located in a 5' position. RNAase 
protection assays and reverse transcription polymerase chain reactions confirmed 
that these unusual RNA molecules represent the most abundant transcript in 
testis. Furthermore, oligonucleotide hybridization and RNAase H digestion proved 
that these Sry RNA molecules are circular. Similar transcripts were detected in 
the testes of mice with Mus musculus musculus, Mus musculus domesticus, and Mus 
spretus Sry genes. The circular RNA is found in the cytoplasm but is not 
substantially bound to polysomes. We suggest that the circles arise from normal 
splicing processes as a consequence of the unusual genomic structure surrounding 
the Sry locus in the mouse.