We want a single-vector mAb expression construct for CHO-K1 stable lines —
heavy + light chain in one transfection, with puromycin selection. We've
had two previous attempts fail at the Golden Gate step because of internal
BsaI sites in codon-optimized variable regions, so zero internal BsaI is
non-negotiable.

Architecture should be: CMV promoter -> signal peptide -> IgG1 heavy chain
-> EMCV IRES -> light chain -> puromycin cassette, around a 7 kb backbone,
assembled in one BsaI Golden Gate reaction. Use trastuzumab variable
domains as the template (well-characterized, public).

Codon-optimize both chains for CHO-K1, target CAI > 0.85, and screen out
all internal BsaI / BsmBI / SapI sites. Use BsaI fusion-site overhangs
from the Potapov 2018 high-fidelity set and confirm no palindromes /
pairwise collisions.

Deliverables we'll need: a junction colony-PCR primer pair per fragment
(Tm-matched, BLAST-checked against CHO-K1 PICRH-1.0), the annotated
GenBank for the full construct, the oligo set as FASTA + an Excel sheet
ready for ordering, and a report with the construct schematic and
fragment-level QC.
