Rv3852 (H-NS) of Mycobacterium tuberculosis Is Not Involved in Nucleoid Compaction and Virulence Regulation.

A handful of nucleoid-associated proteins (NAPs) regulate the vast majority of genes in a bacterial cell. H-NS, the istone-like ucleoid-tructuring protein, is one of these NAPs and protects from foreign gene expression. Though lacking any sequence similarity with H-NS, Rv3852 was annotated as the H-NS ortholog in , as it resembles human histone H1. The role of Rv3852 was thoroughly investigated by immunoblotting, subcellular localization, construction of an unmarked deletion in the genome, and subsequent analysis of the resulting Δ strain. We found that Rv3852 was predominantly present in the logarithmic growth phase with a decrease in protein abundance in stationary phase. Furthermore, it was strongly associated with the cell membrane and not detected in the cytosolic fraction, nor was it secreted. The Δ strain displayed no growth defect or morphological abnormalities. Quantitative measurement of nucleoid localization in the Δ mutant strain compared to that in the parental H37Rv strain showed no difference in nucleoid position or spread. Infection of macrophages as well as severe combined immunodeficient (SCID) mice demonstrated that loss of Rv3852 had no detected influence on the virulence of We thus conclude that Rv3852 is not involved in pathogenesis and is not a typical NAP. The existence of an as yet undiscovered Rv3852 ortholog cannot be excluded, although this role is likely played by the well-characterized Lsr2 protein. is the causative agent of the lung infection tuberculosis, claiming more than 1.5 million lives each year. To understand the mechanisms of latent infection, where can stay dormant inside the human host, we require deeper knowledge of the basic biology and of the regulatory networks. In our work, we show that Rv3852, previously annotated as H-NS, is not a typical nucleoid-associated protein (NAP) as expected from its initial annotation. Rv3852 from has neither influence on nucleoid shape or compaction nor a role in virulence. Our findings reduce the repertoire of identified nucleoid-associated proteins in to four transcription regulators and underline the importance of genetic studies to assign a function to bacterial genes.