3' Untranslated regions (3'UTRs) of messenger RNAs have important roles in post-transcriptional regulation of gene expression and this is partly achieved through binding of specific proteins to sequences or structures within these regions. Previously, replacement of a native luciferase 3'UTR with the human albumin 3'UTR has been found to lead to a 10-fold increase in luciferase reporter activity. In this work we investigated protein binding to the human albumin 3'UTR. Electrophoretic mobility shift and UV cross-linking assays indicate that a 50 kDa protein from Chinese Hamster Ovary (CHO) cells binds to the albumin 3'UTR, and affinity experiments followed by proteomics identified this protein as CUG binding protein 1 (CUG-BP1, also known as CELF1). Deletion analysis of the albumin 3'UTR showed that nucleotides 1-50 and nucleotides 101-150 are not required for binding but that removal of nucleotides 51-100 caused a loss in binding. The results suggest that CUG-BP1 binds to nucleotides 51-100 of the human albumin 3'UTR. In human cells CUG-BP1 binding may thus play a role in regulation of albumin expression and, additionally, it may have a function in post-transcriptional control in CHO cells. (C) 2012 Elsevier Inc. All rights reserved.