Inverted repeats are necessary for circularization of the mouse testis Sry transcript.

Circular non-polyadenylated RNA molecules have been identified as stable transcription products of the human ETS-1 and mouse Sry genes. RNA circularization has been proposed to require two steps. The first step utilizes intramolecular base pairing to produce a transient stem-loop structure. The second step involves splicing a downstream donor splice site (DSS) to a now closely appositioned upstream acceptor splice site (ASS) within the loop. We demonstrate that the presence of long inverted repeats (IR) flanking the mouse Sry gene leads to the formation of the Sry circular transcript in cultured cells. Circularization requires the presence of both IR. As few as 400 complementary nt are necessary for this process. The presence of the IR does not significantly stimulate intermolecular annealing and trans-splicing in vivo.