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A common ancestor of the mammalian transcription factors TCF‐1 and TCF‐1α/LEF‐1 expressed in chicken T cells

Several mammalian T cell‐specific transcription factors have been cloned recently. Two of these, TCF‐1 and TCF‐1α/LEF‐1, display a moderate level of overall sequence similarity, and contain virtually identical versions of a novel type of DNA‐binding domain, the HMG box. To study evolutionary aspects of the TCF transcription factors in relation to lymphoid differentiation, we have isolated chicken TCF clones from a spleen cDNA library. Low‐stringency screening with human probes as well as a polymerase chain reaction‐aided strategy resulted in the cloning of a single chicken TCF (chTCF) gene. Sequence comparison revealed that chTCF contained a TCF‐1α‐like N terminus, and a TCF‐1‐like C terminus. Furthermore, TCF‐1 and TCF‐1α were more homologous to chTCF than to each other. We postulate that chTCF is the direct descendant of a single ancestral gene, which has been duplicated in mammals to yield TCF‐1 and TCF‐1α.