Figure 2.

The TKO expression cassette. Histone 2b or hatching enzyme cis-regulatory elements (A) employed in the cassette are modular and can easily be exchanged with any other regulatory sequence. The start of transcription (B) is set to be at least 20 bp upstream of a canonical Kozak ATG (C) and a nuclear localization sequence (D) that are best fit to sea urchin initiators and codon usage. The heavy- (E) and light-chain (G) variable regions of the anti-P3A2 scFv are separated by an encoded flexible Gly/Ser linker (F). To process, stabilize, and terminate the TKO transcripts, we inserted the SV40 large T 3′ intron (I), polyadenylation (J), and transcriptional termination (K) sequences after the stop codon (H).