The Hepatitis B virus PREbeta (HBV PREbeta) is an RNA structure that is shown to play a role in nuclear export of HBV mRNAs.
The minimal HBV PREbeta structure consists of a 23 nt stem-loop, with a 9 nt apical loop. The conserved stem-loop was predicted within the HBV PRE sequence and confirmed by mutagenesis. The Rfam structure is based on a covariation model. The exact role of this structure in nuclear export has not been determined
References
Hepatitis B virus PRE beta Wikipedia(Text) CC BY-SA