Required for trans-splicing of exons 1 and 2 of the chloroplast encoded psaA mRNA (a group II intron). May be required for stability of the chloroplast RNA-protein complex in which it is found. Part of a 1700 kDa complex that includes the precursor RNA to exon 1 and the tscA RNA. The N-terminal 453 amino acids are dispensable, while the C-terminal 630 amino acids are required for function.