In yeast and plants, low level transcription of a gene is recently revealed to be required to repress the gene. It may account for the widely low level illegitimate transcriptions of tissue-specific genes reported in mammalian cells. This hypothetical link gives insight into both analysis of transcription-associated evolutionary events and further interpretation of the mechanism of small RNA-mediated transcriptional repression. (c) 2005 Elsevier Inc. All rights reserved.