Abstract: A replication initiator protein complex for eukaryotic cells is disclosed which includes protein fractions of about 60 kD and 100 kD size. The protein complex comprises a protein in purified form that is capable of origin-specific DNA binding and ATP-dependent DNA helicase activity. The 60 kD fraction is named RIP60 and is primarily active in origin-specific DNA binding. The 100 kD fraction is named RIP100 and is primarily active as a DNA helicase. The protein complex and its fractions are active only during S phase and thereby commend their investigation and use toward the development of specific diagnostic and therapeutic modalities against pathogens to which cell division is critical. Diagnostic and therapeutic utilities are accordingly proposed, and testing procedures, materials in kit form, recombinant materials and procedures, and pharmaceutical compositions are likewise set forth.