FIG 1.

Design of a circularized spider silk mRNA based on td flanking introns. (A) Schematic of the MaSp1 mRNA circularization mechanism. The MaSp1 coding sequence was cloned between the upstream and downstream td introns, and the whole sequence was transcribed using a T7 promoter. 3′ss, 3′ splice site; 5′ss, 5′ splice site. Upon transcription, the introns form secondary structures, and the 3′ hydroxyl group of guanosine initiates the generation of MaSp1 cmRNA. BSJ, back-splice junction. (B) The ribosome continuously translates spider silk polypeptide by traveling along the round cmRNA.