They bind to DNA [3, 5] preferring AT-rich DNA-sequences  as well as to laminin, hyaluronic acid, heparin, and chondroitin sulphate [5, 6, 12]. The data available so far portray Hlp as multi-faceted proteins, and accordingly a NVP-HSP990 variety of possible functions have been ascribed to Hlp. Hlp were suggested to impact DNA packaging, protection of DNA from enzymatic and non-enzymatic strand breakage , gene regulation , nucleic acid metabolism, non-homologous-end-joining repair , adaptation to Thiazovivin hypoxic conditions ,
induction of dormancy , adaptation to cold shock , adhesion [6, 9, 12, 15–17], cell wall biogenesis  and regulation of growth rate [1, 5, 10]. A role in transition to the non-culturable state and in resuscitation from the non-culturable state was shown in M. smegmatis. Whiteford et al.  investigated the growth characteristics of an M. smegmatis with a deletion of hlp. They found that the mutant showed less aggregation in broth cultures. Furthermore, they observed an increased sensitivity towards Isoniazid. The M. smegmatis mutant also was affected in UV-resistance and resistance towards freezing/thawing. Takatsuka et al.  have recently shown that Hlp has a similar activity to ferritin superfamily proteins and protects DNA by ferroxidase activity. It furthermore captures iron molecules and functions selleck as iron storage protein. Approaches to elucidate the
functions of Hlp by mutagenesis did not always confirm the expected roles of Hlp [2, 15, 21]. Our own attempts to generate a MDP1 deletion mutant had failed. Furthermore and in line with our own experience, Sassetti et al.  had shown by high density mutagenesis that the gene Rv2986c from M. tuberculosis, which is homologous to MDP1 from BCG, is required for optimal growth of M. tuberculosis. We therefore followed the strategy BCKDHB to analyse Hlp functions by down-regulation of Hlp expression by antisense-technique. Advantages of this technique are the possibility to analyse essential genes and to repress genes present in several copies. In mycobacteria the antisense-technique
has been applied to down-regulate ahpC from M. bovis, dnaA from M. smegmatis, FAP-P from M. avium subsp. paratuberculosis or pknF from M. tuberculosis. In a previous study we described the generation of the antisense-strain M. bovis BCG (pAS-MDP1) which carries the plasmid pAS-MDP1 causing a reduction of MDP1 expression in BCG by about 50% . We analysed BCG (pAS-MDP1) with respect to general growth characteristics. The down-regulated BCG grew faster in broth culture and achieved a higher cell mass in the stationary phase. Similarly, growth was enhanced in human and murine macrophage-like cell lines. A further important finding was the reduced protein synthesis occurring under hypoxic conditions . These findings support a role of MDP1 in growth regulation of M. bovis BCG.