Oct Transcription Factors and their Coactivators: Are They Evolutionarily Conserved?
Mara L. Lennard1, Jun-ichi Hikima1,2, Norman W. Miller3, Melanie R. Wilson3, L. William Clem3, and Gregory W. Warr1,2
1 Marine Biomedicine and Environmental Sciences Center, Medical University of South Carolina, Charleston, SC
2 Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC
3 Department of Microbiology, University of Mississippi Medical Center, Jackson, MS
A homologue to the POU domain family protein Oct1 has been cloned from a catfish macrophage library. Phylogenetic analysis indicates that the nucleotide sequence is most closely related to that of zebrafish Oct1, and that the catfish molecule is clearly a homologue of mammalian Oct1. Analysis of the inferred protein sequence indicates a high degree of similarity between catfish Oct1 and both zebrafish and mouse Oct1, ranging from 45% in the putative activation domains to as high as 96% in the DNA-binding POU domain. Surprisingly, upon co-transfection (with an octamer-dependent reporter construct) into both mammalian and catfish B cell lines, catfish Oct1 failed to drive transcription. This lack of activity appears to be independent of cell type or reporter construct. Co-transfection of catfish Oct1 with mammalian Bob-1, a known co-activator, yielded similar results. Subsequent transfection studies revealed that catfish Oct1 is acting as a negative regulator of transcription, consistent with the fact that it binds the cognate octamer motif, as measured by electrophoretic mobility shift assays. Thus, it is concluded that the catfish Oct1 homologue is acting differently than its mammalian counterparts, in that it is transcriptionally inactive on the classical Pol II promoters we have tested. Supported by award #GM62317 from the National Institutes of Health.