The native 299-residue PC isoform matches full-length residues 462–760 and preserves the C-terminal catalytic-site region. The N-terminal glycosyltransferase domain and membrane anchor are absent. Broad activity is not refuted solely from shortening because exostosins possess two chemically distinct domains. PMID:36593275(https://pubmed.ncbi.nlm.nih.gov/36593275/) and PMID:36402845(https://pubmed.ncbi.nlm.nih.gov/36402845/) characterize this division and describe important complex/construct qualifications. The structural studies describe domain-specific chemistry and important expression/activity limitations for isolated constructs; neither assays native fly PC. All five IEAs and the single GO prediction remain UNC pending direct exact-isoform evidence; no wrong-input assertion is made.
The Falcon synthesis integrates fly EXT genetics, morphogen distribution and human EXT1 rescue. These strongly support the full-length Ttv gene function. Its ER/Golgi and copolymerase conclusions do not specifically establish activity or targeting of the native 299-residue PC product, which lacks the N-terminal domain and anchor. The retained C-terminal architecture and primary EXT domain studies support keeping the exact-product glycosyltransferase question open.