mRNA decay is fundamentally involved in the control of the immune response. Dysregulation leads to severe inflammatory diseases and chronic inflammation. This bachelor thesis addresses the regulation of mRNA decay by subcellular localization and posttranslational modification of the mRNA-destabilizing protein Tristetraprolin (TTP). TTP binds as trans-acting RNA-binding protein (RBP) via its tandem zinc finger (TZF) domain to cis-acting AU-rich elements (ARE) within the 3'-UTR of numerous short-lived mRNAs and regulates their stability by additional cooperation with other RNA-binding proteins. TTP activity is regulated in many ways including transcription, mRNA stability, protein stability, subcellular localization and phosphorylation. This complex regulatory network, which is incompletely understood, precisely orchestrates specificity and timing of decay of a large number of inflammatory mRNAs during the entire inflammatory response, with p38 mitogen-activated protein kinase (p38 MAPK) as one of the key regulatory molecules. To further study TTPs functions, bone marrow is taken from WT and TTP deficient mice with ensuing differentiation of myeloid cells into macrophages. Thereafter stimulation of macrophages with bacterial endotoxin lipopolysaccharide occurs with subsequent isolation of proteins. Furthermore the generation of reporter constructs and performance of reporter assays by transfection of 293HEK cells, cell fractioning and TTP protein stability assays follows.