The mouse testis determining gene Sry is expressed in somatic cells of the 
differentiating male gonad as a linear transcript, encoding a transcription 
factor containing an HMG box. In the adult mouse testis, Sry expression occurs 
in meiotic and postmeiotic germ cells. The mouse genomic Sry locus is 
characterized by two arms of a large inverted repeat, flanking a unique region 
that, between an acceptor and a donor splice site, contains a single exon 
encoding the Sry protein. In germ cells from the adult mouse testis, Sry RNA is 
a circular molecule, which is generated by an inverted splicing event that 
utilizes the above-mentioned splice sites. Thus, a circular exon is spliced out 
starting from a large linear RNA precursor containing both arms of the inverted 
repeat, which pair and generate a large stem-loop structure. Using reverse 
transcription-polymerase chain reaction and an RNase protection assay, we have 
now mapped the 5' end of this precursor RNA in the 5' arm of the inverted 
repeat. Gel mobility shift assay and in vitro transcription with nuclear 
extracts from adult germ cells further confirm that a region immediately 5' 
upstream of two transcriptional initiation sites of the precursor RNA contains a 
promoter sequence in which two consensus Sry binding sequences are specifically 
recognized by nuclear factors present in adult germ cells but not in Sertoli 
cells. We also show that the linear precursor of the Sry circular transcript and 
its splicing product are specifically expressed not only in adult germ cells but 
also in male embryonal gonads between 11.5 and 13.5 days postcoitum, immediately 
after the expression of the linear transcript starting from the unique region.