Phylogenomic analysis of the alpha proteasome gene family from early-diverging eukaryotes

We employed a phylogenomic approach to study the evolution of or subunits o f the proteasome gene family from early diverging eukaryotes. BLAST similar ity searches of the Giardia lamblia genome identified all seven or proteaso me genes characteristic of eukaryotes from the crown group. In addition, a PCR strategy for the amplification of multiple or subunit sequences generat ed single or proteasome products for representatives of the Kinetoplastida (Leishmania major), the Parabasalia (Trichomonas vaginalis), and the Micros poridia (Vairimorpha sp., Nosema sp., Endoreticulata sp., and Spraguea loph ii). The kinetoplastid Trypanosoma cruzi and the eukaryote crown group Acan thamoeba castellanii yielded two distinct or proteasome genes each. The pre sence of seven distinct or proteasome genes in G. lamblia, one of the earli est-diverging eukaryotes, indicates that the or proteasome gene family evol ved rapidly from a minimum of one gene in Archaea to seven or more in Eukar ya. Results from the phylogenomic analysis are consistent with the idea tha t the Diplomonida (as represented by G. lamblia), the Kinetoplastida, the P arabasalia, and the Microsporidia diverged after the duplication events tha t originated the or proteasome gene family. A model for the early origin an d evolution of the proteasome gene family is presented.