A novel Krüppel related factor consisting of only a KRAB domain is expressed in the murine trigeminal ganglion

The largest family of zinc-finger (ZnF) transcription factors is that containing the Krüppel-associated box, or KRAB domain. The amino-terminal KRAB domain of these proteins functions as a transcriptional repressor with the downstream ZnF motifs providing DNA-binding specificity. Here we report the identification and characterization of a novel murine Krüppel-related factor (KLF), MIF1, which contains a KRAB domain but lacks a ZnF motif. Western blot analysis identified MIF1-like proteins in the murine trigeminal ganglion (TG) and immunostaining localized these proteins primarily to the cytoplasm of TG neuronal cell bodies. In situ hybridization for Mif1 transcripts confirms the selective expression of Mif1 in TG neurons. Consistent with the non-nuclear localization of MIF1 we could detect no transcriptional repressor activity of the MIF1 protein. However MIF1 appears to be capable of interacting with the co-repressor TIF1β and exhibits transcription repressor activity when fused to yeast GAL4 binding domain protein. Genomic analysis of Mif1 sequence suggests that the Mif1 transcript may result from splicing of a longer KRAB-ZnF containing transcript.