ZF5, which is a Kruppel-type transcriptional repressor, requires the zinc finger domain for self-association

ZF5, which we have cloned as a transcriptional repressor on the mouse c-myc promoter, has the POZ domain at the amino-terminus and the Kruppel-type zinc finger domain at the carboxy-terminus. In this report, we showed that ZF5 has two contradictory functions in transcription: activation of human immunodeficiency virus (HIV) promoter and repression of the HSV thymidine kinase (TK) promoter. The POZ domain contributed to the repressor activity, whereas the active function resulted from the DNA-binding ability of the zinc finger domain. We demonstrated that the POZ domain has a function mediating homomeric protein-protein interaction and this interaction requires the zinc finger domain. Furthermore, the POZ domain decreased the DNA-binding activity of the zinc finger domain. These results can provide evidence indicating the important interaction between the POZ and zinc finger domains.