HETEROCHROMATIC STELLATE GENE-CLUSTER IN DROSOPHILA-MELANOGASTER - STRUCTURE AND MOLECULAR EVOLUTION

The 30-kb cluster comprising close to 20 copies of tandemly repeated S tellate genes was localized in the distal heterochromatin of the X chr omosome. Of 10 sequenced genes, nine contain undamaged open reading fr ames with extensive similarity to protein kinase CK2 beta-subunit; one gene is interrupted by an insertion. The heterochromatic array of Ste llate repeats is divided into three regions by a 4.5-kb DNA segment of unknown origin and a retrotransposon insertion: the A region (similar to 14 Stellate genes), the adjacent B region (approximately three Ste llate genes), and the C region (about four Stellate genes). The sequen cing of Stellate copies located along the discontinuous cluster reveal ed a complex pattern of diversification. The lowest level of divergenc e was detected in nearby Stellate repeats. The marginal copies of the A region, truncated or interrupted by an insertion, escaped homogeniza tion and demonstrated high levels of divergence. Comparison of copies in the B and C regions, which are separated by a retrotransposon inser tion, revealed a high level of diversification. These observations sug gest that homogenization takes place in the Stellate cluster, but that inserted sequences may impede this process.