Cardiff University, Cardiff CF10 3AX, UK). In Drosophila melanogaster differentiation of the male germ cells is accompanied by chromatin rearrangement and activation of the specific genes. These processes are regulated by few transcription factors that belong to two classes, can and aly that form distinct functional complexes. Mechanisms of action of aly and can class transcription factors on gene expression and chromatin state remain unclear. To investigate this question we have built the whole genome binding profile of transcription factor Comr belonging to aly class using the tissue-specific DamID method. Resulting datawere correlated with gene expression in comr (aly class) and can (can class) mutant testes. It was shown that Comr is a direct activator for about 300 testis-specific genes. Furthermore a set of genes revealed decreased expression in comr mutants but did not bind Comr protein, suggesting the existence of secondary regulation. Indeed, among the Comr gene targets we found a gene coding an uncharacterized transcription factor that could be a secondary participant in the genetic pathway in spermatocytes. These date allowed us to advance a model of gene activation needed for male gametes differentiation in D. melanogaster.