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). Can inadvertently accommodate and process non-cognate amino acids such as cysteine and alanine. ATP + L-proline + tRNA(Pro) = AMP + diphosphate + L-prolyl-tRNA(Pro) Inhibited by high concentrations of prolinamide. Homodimer. The dimer is functionally asymmetric: only one of the two active sites at a time is able to form prolyl-adenylate, and only one tRNA molecule binds per dimer. 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. Was originally (PubMed:10642548, PubMed:10869184 and PubMed:11141055) thought to have both prolyl- and cysteinyl-tRNA synthetase activities (ProCysRS). However, recent biochemical and structural studies show that ProRS misaminoacylates tRNA(Pro) with cysteine but is unable to aminoacylate tRNA(Cys). These conflicting results may be due to the fact that much of the previous work was done with unfractionated tRNA. According to PubMed:12130658, ProRS is unable to edit the misacylated Cys-tRNA(Pro) and Ala-tRNA(Pro), whereas according to PubMed:11408489, it hydrolyzes Ala-AMP and Ala-tRNA(Pro) by 'pretransfer' and 'posttransfer' editing activities, respectively.