THE INFLUENCE OF THE Chd1 CHROMATIN ASSEMBLY AND REMODELING FACTOR MUTATIONS ON DROSOPHILA POLYTHENE CHROMOSOME ORGANIZATION.

Chromatin assembly is a fundamental process that is essential for chromosome duplication subsequent to DNA replication. In addition, histone removal and incorporation take place constantly throughout the cell cycle in the course of DNA-utilizing processes, such as transcription, damage repair or recombination. In vitro chromatin assembly requires the concerned action of histone chaperones and ATP-utilizing chromatin assembly factors. ATP-dependent chromatin assembly and remodeling factor CHD1 (Chromo-ATPase/Helicase-DNA-binding protein 1) is involved in multiple cellular processes, such as the replication independent assembly of nucleosomes containing the variant histone H3.3, regulation of transcription initiation, elongation and termination; determination of steam cell pluripotency and in cancer development. We have shown that mutations in Drosophila Chd1 gene induce a decondensation of the male X chromosome, similar to that induced by mutations in the iswi nucleosome remodeling factor. An effect of Chd1 null mutation can be increased by deficiency of one of the genes, encoding variant histone H3.3, His 3.3 B, suggesting that the role of CHD1 in the control of male X chromosome organization can be mediated by CHD1 activity in H3.3 histone deposition and exchange.