Addressing the possibility of a histone-like code in bacteria.

Carabetta, Valerie J

Acetylation was initially discovered as a post-translational modification (PTM) on the unstructured, highly basic N-terminal tails of eukaryotic histones in the 1960s. Histone acetylation constitutes part of the "histone code," which regulates chromosome compaction and various DNA processes, such as gene expression, recombination, and DNA replication. In bacteria, nucleoid associated proteins (NAPs) are responsible these functions, in that they organize and compact the chromosome, and regulate some DNA processes. The highly conserved, DNABII family of proteins are considered functional homologs of eukaryotic histones, despite having no sequence or structural conservation. Within the past decade, a growing interest in Nε-lysine acetylation led to the discovery that hundreds of bacterial proteins are acetylated with diverse cellular functions, in direct contrast to the original thought that this was a rare phenomenon. Similarly, other previously undiscovered bacterial PTMs, like serine, threonine and tyrosine phosphorylation, have also been characterized. In this review, the various PTMs that were discovered among DNABII family proteins, specifically HU orthologs, from large-scale proteomic studies will be discussed. The functional significance of these modifications and the enzymes involved will also be addressed. The discovery of novel PTMs on these proteins, begs the question: Is there a histone-like code in bacteria?