## 1 Introduction
The UspA protein is a serine and threonine autophosphorylating protein whose phosphorylation is highly dependent on the TypA tyrosine phosphoprotein, which is activated in response to stasis [10; 15]. A possible explanation for the importance of this feature is the ability of UspA to regulate the detrimental effects of other proteins in growth-arrested cells. It was suggested that UspA in coercion with the \(\alpha\)591 tyrosine phosphoprotein degrades such proteins by phosphorylation tagging [10]. Some studies also suggested that the increases in UspA phosphorylation may be the factor responsible for the acidification of a minimum of six proteins during the early stages of growth arrest in cells [10; 16]. Other studies suggested that the absence of this protein increases sensitivity when cells are exposed to mitomycin C and UV irradiation, since it forms part of the RecA-dependent DNA protein and repair system [17]. Subsequent analysis of the _E. coli_ genome led to the discovery of five more use family genes in bacteria, _uspC_, _uspD_, _uspE_, _uspF_, and _uspG_, which are all associated with adhesion, motility, and resistance to oxidative stress [15; 18]. Together with _uspA_, _uspD_ not only defends against agents responsible for superoxide generation but is also a regulator of intracellular iron. _uspE_ and _uspD_ on the other hand, are essential for cellular motility, which takes place at the expense of cell adhesion through _uspE_ and _uspD_ genes, whose link to cell adhesion has been demonstrated via electron microscopy. However, _uspF_ and _uspD_ exhibit the exact opposite of _uspE_ and _uspD_ effects [15; 19; 20]. All this proves the evolvement of USPs to exhibit various physiological roles within the cell for its survival, defense and escape from cellular stress (Figure 1) [15]. Since then, through the sequencing of genomes, the presence of universal stress proteins have not only been located in bacteria, but were observed to be widely distributed in archaea, plants, metazoans, as well as in yeast, fungi, invertebrate, and protist genomes, forming a significant part of their defense systems against various forms of stress [17; 18; 21]. The presence of USPs has also been observed in various diseases, mostly in the pathogens responsible for them. For the most part, a significant component of pathogen virulence to the host is dependent on stress resistance [17; 21]. This is because colonization and pathogenicity in the host largely depends on overcoming various host responses, such as depletion of nutrients and the presence of reactive oxygen species. The existence of USPs in certain microorganisms has shown that they are involved in contributing to pathogen colonization as well as the establishment of persistent infections in humans. Examples of these include USPs in _Acinetobacter baumannii_, _Salmonella typhimurium_, as well as Usp isoforms in _Mycobacterium tuberculosis_ and in various strains that cause cystic fibrosis (CF) and schistosomiasisomiasis [3; 22]. Although the importance of USPs has been highlighted in the literature and a considerable amount of work has been done in studying the regulation and physiology of these proteins, the molecular mechanisms by which they provide protection and stress resistance remain elusive [3; 22; 23]. This paper attempts to draw more attention to this ubiquitous and widely distributed group of proteins by elucidating proposed molecular mechanisms in context of their contribution to pathogen survival and infection persistence.