Isolation and characterization of Rac1 pseudogenes (ψ ₁Rac1- ψ ₄Rac1) in the human genome

Ras-related C3 toxin substrate 1 (Rac1) is a small Rho-GTPase with important functions in fundamental cellular processes such as cytoskeleton rearrangements, signal transduction, cell cycle progression and malignant transformation. Using Rac1 primer, we identified a 5.5-kb DNA sequence on chromosome 4 (Chr. 4) in the human genome, containing the intronless protein coding sequence of Rac1. Sequence analysis revealed features of a processed pseudogene, which we named ψ ₁Rac1, that could be detected by Southern blot and polymerase chain reaction (PCR) on genomic DNA. A ψ ₁Rac1 pseudogene transcript was not detected by reverse transcription-polymerase chain reaction (RT-PCR), nor had the ψ ₁Rac1 promoter any transcriptional activity. In addition, three other intronless pseudogenes of Rac1 on chromosomes 4, 13 and X were identified (ψ ₁Rac1-ψ ₄Rac1) sharing an 86-96% sequence similarity with Rac1. Neither RT-PCR with pseudogene specific restriction enzymes, nor the sequencing of 130 cDNA clones from benign and malignant breast tissue and cell lines, detected the transcription of any of the Rac1 pseudogenes (ψ ₂Rac1-ψ ₄Rac1). Existence of Rac1 pseudogenes should be taken into consideration when analyzing genomic alterations of the human Rac1 gene.