Small nuclear (sn)-RNAs are short, intronless and non polyadenylated RNAs that are required for critical cellular functions including splicing. Like protein-coding genes snRNA genes are transcribed by Pol II. However, there are significant differences in transcription and processing between mRNAs and snRNAs. 3' end formation of the human snRNAs occurs in a series of steps starting with cotranscriptional RNA processing which is directed by the snRNA gene-specific 3' box rather than the poly(A) site as found in protein-coding genes. Uguen and Murphy (2003) recently obtained accurate 3'end formation of synthetic RNA substrates containing the 3' box of the human U1 RNA genes in vitro in the absence of ongoing transcription. This system requires S1 nuclease digestion of processing products. The first chapter of this thesis reports the development of a faster and easier to handle in vitro processing system where the processing products are monitored directly by the use of radiolabelled RNA. Until recently, the factors involved in snRNA 3'end formation remained unknown. In 2005, Baillat et a/. described a multi-protein complex called Integrator which is necessary for snRNA 3'end formation. I have further investigated the role of Integrator components in snRNA 3'end processing. I have shown that a smaller complex, 240 kDa, is sufficient for in vitro processing, suggesting that only a fraction of the Integrator complex is necessary for correct snRNA 3'end formation in vitro. In addition, several candidate proteins were tested and ruled out as factors involved in snRNA 3'end formation.