The invention provides human protein complexes with endonuclease activity. In particular, the invention provides human protein complexes with tRNA splicing endonuclease activity and/or 3' end pre-mRNA endonuclease activity. The invention also provides a splice variant of human Sen2, namely human Sen2deltaEx8, and human protein complexes comprising human Sen2deltaEx8. The human Sen2deltaEx8 complexes have pre-tRNA cleavage activity and/or 3' end pre-mRNA endonuclease activity. The invention also provides human protein complexes with pre-ribosomal RNA cleavage activity. The invention also provides antibodies that immunospecifically bind to a complex described herein or a component thereof, and methods of diagnosing, preventing, treating, managing or ameliorating a disorder utilizing such antibodies. The present invention also provides methods utilizing the complexes described herein, inter alia, in screening, diagnosis, and therapy. The invention further provides methods of preparing and purifying the complexes. The present invention further provides methods of identifying a compound that modulates the expression of a component of a complex described herein, the formation of a complex described herein or the activity of a complex described herein, and methods of preventing, treating, managing or ameliorating a disorder, such as a proliferative disorder, or a symptom thereof utilizing a compound identified in accordance with the methods.