Satellite DNAs are major building elements of pericentromeric and centromeric heterochromatinin many eukaryotic species, and in certain species they account for the majority of genomicDNA. Wide evolutionary distribution, presence of functional elements such as promoters andtranscription factor binding sites within some satellite DNA sequences as well as transcriptionalactivity of many satellites has led to the assumption that they might also act as regulatoryelements of gene expression. The aim of the proposed project is to investigate the gene-regulatory role of TCAST satellite DNA in insect T. castaneum. Short stretches of TCAST havebeen mapped in the close vicinity of numerous genes within euchromatin and environmentallysusceptible transcription of TCAST satellite DNA was shown. The results will for the first timedemonstrate role of satellite DNAs in the modulation of protein-gene expression and reveal themolecular mechanism of their gene-regulatory activity.