PCAF catalyzes tha acetylation of spermidine to N8-acetylspermidine and regulates its acetylating activity on histones

Post-transcriptional histone acetylation is a well known process playing a crucial role in chromatin assembly and transcription. Here, we report that PCAF, a highly conserved histone acetyltransferase (HAT), can efficiently catalyze acetylation of spermidine to N8-acetylspermidine, at low concentration. Remarkably, we found that spermidine at higher concentration can also inhibit PCAF HAT activity directed against histone H3 in vitro, confirming the in vivo data referred by Eisenberg et al. on the spermidine induced inhibition of H3 acetylation. Surprisingly when we performed HAT assay experiments at low spermidine concentration we observed an activating effect on PCAF on H3 acetylation. Our data indicate that high spermidine concentration may establish a competition with histone. The acetylation of spermidine to N8-acetylspermidine probably determines an interaction with a regulatory site of the enzyme, inducing a new configuration of PCAF that modify its HAT activity.