This invention relates to a peptide or protein capable of converting a transcription factor into a transcriptional repressor, a gene encoding such peptide or protein, a chimeric protein in which the aforementioned peptide or protein is fused to a transcription factor, a chimeric gene in which the gene encoding a peptide or protein is fused to a gene encoding a transcription factor, a recombinant vector having such chimeric gene, and a transformant comprising such recombinant vector. The peptide of the invention that is capable of converting a transcription factor into a transcriptional repressor is very short. Thus, it can be very easily synthesized, and it can effectively and selectively repress the transcription of a specific gene. Accordingly, such gene is applicable to and useful in a wide variety of fields, such as repression of the expression of cancerous genes and regulation of the expression of genes encoding pigment-metabolic enzymes.