Recent observations that alternative pre-mRNA 3' end processing results in a global, decreased susceptibility of mRNAs to miRNA-dependent inhibition in dividing cells including cancer cells caused renewed interest in the 3' end processing of mRNAs. The mechanism by which a systematic change in the use of proximal versus distal polyadenylation sites in resting and dividing cells occurs is not known. The previous work within the scope of our grant contributes to the elucidation of the dynamics of 3’ end processing factors within the 3' end processing complex itself and also within the transcriptomes of selected mammalian cell systems. This is of obvious relevance to the currently unsolved puzzles concerning systematic changes in the 3’ end processing and polyadenylation in relation to the cellular state. In collaboration with the Zavolan group at the Biozentrum, we recently initiated a study of binding sites of various 3’ end processing factors in a number of cell types and under various conditions. Our preliminary results are very promising in that the binding sites that we identified reflect the known sequence specificities of the factors that we studied and their relative location agrees with prior findings. We therefore request that funding for our project is continued in order to complete these studies which will further the understanding of how 3’ end processing interfaces with other cellular processes such as transcription, alternative splicing and polyadenylation as well as with the susceptibility to post-transcriptional regulation. A second part of the project is aimed at the elucidation of the structure of the cleavage and polyadenylation factor CPF, the key protein complex involved in the 3’ end processing of yeast pre-mRNAs and snoRNAs. In collaboration with Professor Holger Stark (MPI Göttingen) we plan to achieve a high-resolution structure by cryo-electron microscopy.