An example of intron junctional sliding in the gene families encoding squalene monooxygenase homologues in Arabidopsis thaliana and Brassica napus

Sequences of three Arabidopsis thaliana and two Brassica napus cDNAs encodi ng squalene monooxygenase homologues (Sqp1 and Sqp2) are reported. Southern analysis confirmed that these cDNAs are derived from small gene families i n both species. Expression analysis indicates that Sqp1 genes in B. napus a re strongly expressed in leaves but not roots or developing seeds. Comparis on of cDNA and genomic sequences indicate that the 3' splice site of an int ron in these genes has undergone junctional sliding. The evolutionary signi ficance of this phenomenon is discussed.