Localization of zinc finger Mok2 gene to mouse chromosome 6, a new region of homology with human chromosome 19

The zinc finger transcription factor, MOK2, negatively modulates expression of the interphotoreceptor retinoid-binding protein gene, IRBP

The human and murine MOK2 orthologue genes encode Krüppel/TFIIIA-related zinc finger proteins, which are factors able to recognize both DNA and RNA through their zinc finger motifs. MOK2 proteins have been shown to bind to the same 18-base pair (bp)-specific sequence in duplex DNA. This MOK2-binding site was found within introns 7 and 2 of human PAX3 and interphotoreceptor retinoid-binding protein (IRBP) genes, respectively. As these two genes are expressed in the brain as MOK2, we have suggested that PAX3 and IRBP genes are two potentially important target genes for the MOK2 protein. In this study, we focused our attention on IRBP as a potential MOK2 target gene. Sequence comparison and binding studies of the 18-bp MOK2-binding sites present in intron 2 of human, bovine, and mouse IRBP genes show that the 3'-half sequence is the essential core element for MOK2 binding. Very interestingly, 8-bp of this core sequence are found in a reverse orientation, in the IRBP promoter. We demonstrate that MOK2 can bind to the 8-bp sequence present in the IRBP promoter and repress its transcription when transiently overexpressed in retinoblastoma Weri-RB1 cells. In the IRBP promoter, it appears that the TAAAGGCT MOK2-binding site overlaps with the photoreceptor-specific CRX-binding element. We suggest that MOK2 represses transcription by competing with the cone-rod homeobox protein (CRX) for DNA binding, thereby decreasing transcriptional activation by CRX. Furthermore, we show that Mok2 expression in the developing mouse and in the adult retina seems to be concordant with IRBP expression.

Physical and genetic maps of the deafwaddler region on distal mouse Chr 6

The deafwaddler (dfw) mutation, displaying motor ataxia and profound deafness, arose spontaneously in a C3H/HeJ colony and was mapped previously to distal mouse Chr 6. In this study, a high-resolution genetic map was generated by positioning 10 microsatellite markers and 5 known genes on a 968-meioses intersubspecific backcross segregating for dfw [(CAST/Ei(-)+/+ x C3HeB/ FeJ-dfw/dfw) x C3HeB/FeJ-dfw/dfw], giving the following marker order and sex-averaged distances: D6Mit64-(0.10 + 0.10 cM)-Pang-(1.24 + 0.36 cM)-Itpr1-(0.62 + 0.25 cM)-D6Mit108-(0.52 + 0.23 cM)-D6Mit54-(0.21 + 0.15 cM)-D6Mit23, D6Mit107, D6Mit328-(0.72 + 0.27 cM)-D6Mit11-(0.21 + 0.15 cM)-dfw-(0.93 + 0.31 cM)-Gat4, D6Mit55-(0.10 + 0.10 cM)-D6Mit63-(0.31 + 0.18 cM)-Syn2-(0.62 + 0.25 cM)-D6Mit44 (Rho). Female and male genetic maps are similar immediately surrounding the dfw locus, but show marked differences in other areas. A yeast artificial chromosome-based physical map suggests that the closest markers flanking the dfw locus, D6Mit11 (proximal) and Gat4, D6Mit55 (distal), are contained within 650-950 kb. The human homologues of the flanking loci Itpr1 (proximal) and Syn2 (distal) map to chromosome 3p25-p26, suggesting that the human homologue of the dfw gene is located within this same region.

Human and mouse MOK2 proteins are associated with nuclear ribonucleoprotein components and bind specifically to RNA and DNA through their zinc finger domains

The human and murine MOK2 ortholog genes that are preferentially expressed in brain and testis tissues encode two different Krüppel-like zinc finger proteins. In this paper, we show that the MOK2 proteins are mainly associated with nuclear ribonucleoprotein components, including the nucleoli and extranucleolar structures, and exhibit specific RNA homopolymer binding activities. Moreover, we have identified an identical 18-bp specific DNA binding sequence for both MOK2 proteins using a pool of random sequence oligonucleotides. The DNA binding domain is localized in the seven adjacent zinc finger motifs, which show 94% identity between human and murine proteins. Taken together, these results establish that the MOK2 proteins are able to recognize both DNA and RNA through their zinc fingers. This dual affinity and the subnuclear localization suggest that MOK2 may play roles in transcription, as well as in the posttranscriptional regulation processes of specific genes.