Unusual evolutionary conservation of 5S rRNA pseudogenes in Aspergillus nidulans: similarity of the DNA sequence associated with the pseudogenes with the mouse immunoglobulin switch region.

All Aspergillus nidulans 5S rRNA pseudogenes known so far are the result of integration of an approx. 0.2-kbp-long DNA sequence into the 5S rRNA genes. This sequence, called block C, is present in at least five copies in the A. nidulans genome and seems to be associated either with 5S rRNA genes or pseudogenes. In contrast to the 78% sequence conservation of the C-block in pseudogenes, the truncated 5' halves of the pseudogenes are very highly conserved (96.9-100%). We postulate that the 5S rRNA pseudogenes are still a subject of concerted evolution. The C-block sequence shows similarity to the switch region of the mouse heavy chain immunoglobulin gene. A characteristic motif GGGTGAG is repeated several times in both sequences; the sequence conservation is 63%.