The function of eukaryotic histone deacetylase (HDAC) has been extensively 
studied for its critical role in transcriptional regulation and carcinogenesis. 
However that of the prokaryotic counterpart remains largely unknown. Recently, 
we cloned HDAC-like protein in Thermus caldophilus GK24 (Tca HDAC) from a 
genomic library of the microorganism based on homology analysis with human 
HDAC1. To explore the function of Tca HDAC in mammalian cells, Tca HDAC gene 
expressing vector was transfected into a human fibrosarcoma cell line, HT1080. 
Tca HDAC was mainly localized in nuclei of the mammalian cells as a human HDAC1 
was, due to an N-terminal HDAC association domain. We further generated 
histidine-substituted Tca HDAC mutants and investigated their role in 
biochemical and cellular activity of the enzyme. Tca HDAC mutants exhibited 
dramatic loss of enzymatic activity and conditioned media (CM) from HT1080 cells 
transfected with mutant Tca HDAC was unable to stimulate angiogenic phenotypes 
of endothelial cells in vitro whereas that of wild Tca HDAC did. Collectively, 
these results demonstrate that a prokaryotic histone deacetylase from T. 
caldophilus GK24 is functionally active in mammalian cells and its function in 
gene expression is conserved from prokaryotes to eukaryotes.