What type of chromatin modification is associated with increasing promoter activity?

Histone acetylation is the modification that is associated with increasing promoter activity. This modification involves the addition of an acetyl group to the lysine residues on the histones, which leads to a more relaxed chromatin structure known as euchromatin. The relaxed state of chromatin allows for greater accessibility of the DNA to transcription factors and RNA polymerase, facilitating the binding and initiation of transcription at the promoter region.

In contrast, other types of modifications like DNA methylation generally lead to gene repression by causing the chromatin to become more tightly packed, inhibiting the transcriptional machinery's access to the DNA. Histone methylation can either activate or repress transcription depending on the context and specific residues that are methylated. Histone phosphorylation also plays roles in various cellular processes, including signaling and the regulation of chromatin structure, but it is not as directly associated with the activation of transcription at promoters as histone acetylation is.

Thus, histone acetylation stands out as the modification directly linked to enhancing promoter activity by promoting a more open chromatin configuration, thereby supporting active transcription.