We have been studying the molecular organization of the large heterochromatic chromosome (which contains almost nothing but the satellite DNAs) of Drosophila nasutoides in order to understand structural and functional significance of heterochromatin in general. We examined the structure - nucleosome arrangements - of satellite DNA bearing chromatin and main band DNA bearing chromatin and found that the former has fewer nucleosomes per given length of chromatin. We extend this study further by looking at nuclease digestion behavior of these chromatins. Another project is to study sequence divergence of a satellite DNA in this Drosophila. The satellite II shows 17% sequence divergence between repeat units and contains restriction sites of EcoRI, AluI and Sa1I in such a way that all these enzymes produce multimeric fragments of 96 base pairs and its higher multiples. We cloned EcoRI fragments into the phage lambda in order to examine the arrangements of these three restriction sites. Electrophoretic analysis of restriction enzyme digests of cloned satellite fragments are in progress.