The aim of this PhD work was the purification of a complete and functional pre-mRNA 3' end processing cleavage complex. The complex should be assembled on an immobilised RNA and purified via RNA affinity methods; the tobramycin affinity selection method and another RNA affinity chromatography approach, based on the interaction of the BoxB RNA element from Phage λ and the antiterminator protein N. Several attempts were made to adapt these methods for the cleavage complex. Nevertheless, it was not possible to purify a pre-mRNA cleavage complex. Thus we changed the tools for the affinity purification of the cleavage factors from human cells, for the reconstitution of the cleavage reaction. All known sub-complexes of the 3' end processing cleavage complex were affinity purified via his8-flag-tag, analysed by mass spectrometry, western blot and activity assays. Purification via different subunits revealed that CF Im probably is a multimeric protein complex, consisting at least two of each of the two subunits. Mass spectrometry analysis of the CstF HF-64K preparation revealed the copurification of some CPSF subunits. This demonstrates the tight interaction of CPSF and CstF. CF IIm was purified via HF-hClp1 and contained three proteins of the tRNA splicing endonuclease complex in addition to hClp1 and hPcf11. hClp1 is probably present in two complexes, the tRNA splicing endonuclease complex and CF IIm. CPSF was purified via tagged CPSF-73K and contained all known subunits, and the associated factors hFip1 and symplekin. These affinity purified proteins were used together with recombinant poly(A) polymerase in an attempt to reconstitute the cleavage complex. Although a set of different experimental conditions were tested, cleavage activity was not observed.