Catalyzes the attachment of proline to tRNA(Pro) in a two-step reaction: proline is first activated by ATP to form Pro-AMP and then transferred to the acceptor end of tRNA(Pro). ATP + L-proline + tRNA(Pro) = AMP + diphosphate + L-prolyl-tRNA(Pro) Homodimer. Consists of three domains: the N-terminal catalytic domain, the anticodon-binding domain and the C-terminal extension. Belongs to the class-II aminoacyl-tRNA synthetase family. ProS type 3 subfamily.