Some properties of HU are modified after the infection of Escherichia coli by bacteriophage T4.

Escherichia coli HU, an abundant, nucleoid-associated, DNA-binding protein, plays a role in several biological processes including DNA replication. Many other bacteria have well-conserved HU homologs, and there are several more-distantly related members of the family, including TF1, encoded by Bacillus subtilis phage SPO1. We have asked whether coliphage T4, like SPO1, encodes an HU homolog or whether it alters the properties of host HU. We have been unable to detect a T4-specified HU homolog, but we have shown that E. coli HU extracted from phage-infected cells differs in some properties from that extracted from uninfected cells. First, HU from uninfected cells inhibits a reconstituted T4 DNA replication system, whereas HU from infected cells does not. Second, HU from infected cells appears to bind a T4-encoded polypeptide, as shown by coimmunoprecipitation. We propose that such binding alters HU function in T4-infected cells.