Nature and structure of human genes that generate retropseudogenes

The human genome is estimated to contain 23,000 to 33,000 retropseudogenes. To study the properties of genes giving rise to these retroelements, we co mpared the structure and expression of genes with or without known retropse udogenes. Four main features have emerged from the analysis of 181 genes as sociated to retropseudogenes: Reverse-transcribed genes are (I) widely expr essed, (2) highly conserved, (3) short, and (4) CC-poor. The first two prop erties probably reflect the Fact that genes giving rise to retropseudogenes have to be expressed in the germ-lille. The two latter points suggest that reverse-transcription and transposition is more efficient for short CC-poo r mRNAs. In addition, this analysis allowed us to reject previous hypothese s that widely expressed genes are CIC rich. Rather, globally, genes with a wide tissue distribution are GC poor.