DNA-related activities such as transcription, replication, and repair are associated with modifications in the structure of chromatin and nucleosomes. The transcriptional coactivators CBP/p300 and PCAF/GCN5 are present in a multiprotein complex and function in concert with a variety of transcriptional factors. HMGB1 is a nonhistone DNA-binding protein that functions as a structural cofactor critical for proper transcriptional regulation in somatic cells. It promotes DNA bending and facilitates the binding of several regulatory protein complexes to DNA. It is now well established that coactivators are brought to the promoter of target genes through the interaction with specific DNA-binding factors, and act as acetyltransferases that acetylate histones and transcriptional factors. We have recently cloned Schistosoma mansoni cDNAs enconding two acetyltransferases: SmCBP/p300 and SmGCN5. We showed by in vitro acetylation assays that the HAT catalytic domain of both SmCBP and SmGCN5 were sufficient to promote specific acetylation of histones H3 and H2A, as well as acetylation of SmHMGB1.  In order to further characterize the acetylation patterns by these enzymes, we used synthetic peptides and mass spectrometry analysis. We were able to map the lysine 14 of histone H3 as the substrate for SmCBP/p300 and SmGCN5. Since it is known that acetylation of lysine 14 in Histone H3 is directly related to transcription activation, we assumed that both schistosome acetyltransferases play a role in gene activation. Our assumption was reinforced with the data obtained by electron microscopy. In this experiment we clearly showed that antibodies against SmGCN5 hybridized in the nuclei of schistosome cells. Moreover, these specific hybridizations occurred mainly in regions of the euchromatin, which is the active transcriptional form of the chromatin.