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 encoding squalene monooxygenase homologues (Sqp1 and Sqp2) are reported. Southern analysis confirmed that these cDNAs are derived from small gene families in both species. Expression analysis indicates that Sqp1 genes in B. napus are strongly expressed in leaves but not roots or developing seeds. Comparison of cDNA and genomic sequences indicate that the 3 splice site of an intron in these genes has undergone junctional sliding. The evolutionary significance of this phenomenon is discussed.