Heterochromatin is a fundamental component of eukaryotic genomes and it is essential for genome integrity and cell-fate control. Heterochromatin dysfunction results in chromosome instability and a failure in developmental lineage specification. Therefore, studying the establishment of heterochromatin formation is important. The key factors functioning in heterochromatin formation are well characterized, but the regulatory mechanisms are not fully understood. By using genetic screens for suppressor of PEV (Su(var)) modifier mutations, novel factors regulating heterochromatin are discovered. My project is focused on novel discovery of Su(var) genes in Drosophila melanogaster and characterize their molecular functions in establishing heterochromatin formation.