ATF1, CREB, and CREM constitute a subfamily of the basic leucine zipper transcription factors, and they activate gene expression by binding as homo- or heterodimers to the cAMP response elements (CRE) (consensus: 5'-GTGACGT[AC][AG]-3'). ATF1 (activating transcription factor 1) plays important roles in cell survival and proliferation [, ]. It is required for the development of preimplantation embryos [].
This entry represents the second LIM domain of Four and a half LIM domains protein 5 (FHL5, also known as ACT), which belongs to the CREB/CREM family of transcription factors. FHL5 is highly expressed in male germ cells and is required for post-meiotic gene expression. It associates with CREM and confers a powerful transcriptional activation function []. Activation by CREB has known to occur upon phosphorylation at an essential regulatory site and the subsequent interaction with the ubiquitous coactivator CREB-binding protein (CBP). However, the activation by FHL5 is independent of phosphorylation and CBP association. It represents a new route for transcriptional activation by CREM and CREB [, ].LIM domains are 50-60 amino acids in size and share two characteristic zinc finger motifs. The two zinc fingers contain eight conserved residues, mostly cysteines and histidines, which coordinately bind to two zinc atoms. LIM domains function as adaptors or scaffolds to support the assembly of multimeric protein complexes [, , ].
