Posttranslational modification of E. coli histone-like protein H-NS and bovine histones by short-chain poly-(R)-3-hydroxybutyrate (cPHB).

Short-chain poly-(R)-3-hydroxybutyrate (cPHB), a highly flexible, amphiphilic molecule with salt-solvating properties, is a ubiquitous constituent of prokaryotic and eukaryotic cells, wherein it is mainly conjugated to proteins. The solvating properties and cellular distribution of cPHB suggest it may be associated with proteins that bind and/or transfer DNA. Here we examine Escherichia coli protein H-NS and calf thymus histones, H1, H2A, H2B, H3, and H4, for the presence of cPHB. The proteins are related in that all bind to DNA and are implicated in the compact organization of the chromosome. The presence of cPHB in E. coli H-NS was first detected in Western blots of two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels of total cell proteins, probed with anti-cPHB IgG, and then by Western blot analysis of the purified protein. Western blot analysis of the calf thymus histones indicated that each contained cPHB. The presence of cPHB in H-NS and histones was confirmed by chemical assay. The in vivo size of conjugated cPHB could not be established due to the lack of standards and degradation of cPHB during protein purification and storage. The molecular characteristics of cPHB and its presence in histone-like and histone proteins of diverse organisms suggest it may play a role in DNA binding and/or DNA organization.