Abstract: Recombinant nucleic acids which encode aminoacyl-tRNA sythetases of pneumocystis origin or portions of such enzymes, have been isolated. These nucleic acids can be used to make expression constructs and transformed host cells for the production of pneumocystis aminoacyl-tRNA synthetases. They can also be used in the further isolation of nucleic acids related by DNA sequence similarities, which also encode pneumocystis aminoacyl-tRNA synthetases, or portions thereof. A further embodiment of the invention is antisense nucleic acid which can hybridize to the nucleic acid which encodes the aminoacyl-tRNA synthetase of pneumocystis. The invention also relates to enzymes, isolated and/or recombinant pneumocystis aminoacyl-tRNA synthetases. Antibodies which bind to these enzymes can be made and can be used in the purification and study of the enzymes.