- The high mobility group (HMG) proteins are nonhistone chromosomal proteins that participate in diverse nuclear activities including chromatin structure and gene regulation. We previously studied the biochemistry of the maize HMGA protein and its role in transcriptional regulation during maize endosperm development. Here, we extended our study and showed that a strong binding of ZmHMGA to AT-rich DNA requires at least three AT-hook motifs; two motifs showed a significant reduction whereas a single motif was not sufficient for binding. CDK phosphorylation sites situated between AT-hook3 and AT-hook4 were strongly phosphorylated by a SUC1-associated kinase; no in vitro phosphorylation is evident for the AtHMGA protein. Phosphorylation of ZmHMGA reduced its binding to AT-rich DNA in vitro. The maize HMGA protein fused to GFP was localized in the nucleus of transgenic Arabidopsis plants tending to concentrate within the nucleolus. Localization to the nucleolus was conferred by the C-terminal portion of the protein containing the AT-hooks. ZmHMGA was acetylated in vitro on its N-terminal globular domain by the human PCAF acetyltransferase. Our results suggest that ZmHMGA participates in nucleolar function and that its role may be regulated posttranslationally by phosphorylation and acetylation.