Required for trans-splicing of exons 2 and 3 of the chloroplast encoded psaA mRNA (a group II intron). It is not known if this protein has pseudouridine activity; mutation of the potential active site residue does not cause loss of trans-splicing. Possibly associated with other factors required for trans-splicing. Associated with low density membranes. Belongs to the pseudouridine synthase TruB family.