Paralogous Stellate and Su(Ste) repeats: evolution and ability to silence a reporter gene

The X-linked Stellaterepeats, encoding a putative regulatory subunit of protein kinase CK2, are expressed in XO male testes. The Y-linked, testes-expressed paralogous Su(Ste) repeats are thought to be suppressors of Stellatetranscription. The unique, testis-expressed euchromatic gene was suggested to be an ancestor of the both types of amplified paralogous repeats. A Su(Ste)-like orphon was localized on a Y chromosome, outside of the Su(Ste) cluster. Several diagnostic molecular markers peculiar for the both types of diverged Stellateand Su(Ste) units were detected in the orphon sequence. The orphon was suggested to be a close relative of the immediate ancestor of both types of paralogous repeats which initiated evolution on the Y chromosome. Selection pressure on the level of translation was shown as a driving force in the evolution of Su(Ste) repeats, which are considered as more ancient derivatives of the ancestor euchromatic gene than Stellaterepeats. In a vicinity of 12E Stellatecluster the undamaged, recently originated euchromatic Stellateorphon was found at 12D, providing the poly(A) signal for the bendlessgene. P-element mediated transformations reveal that the fragments of cloned Stellateand Su(Ste) clusters are able to induce variegation of a reporter mini-whitegene. The observed variegation phenomenon has peculiar features: a significant increase of trans-activation of a reporter mini-whitegene in homozygous stat; absence of effects of several conventional modifiers of position effect variegation (PEV) and independence of a severity of variegation on a distance between insertion and centromere region.