Читать книгу Structure and Function of the Bacterial Genome - Charles J. Dorman - Страница 45

Sequence‐dependent DNA‐binding proteins such as MaoP, MatP, SeqA, and SlmA play important roles in the organisation of the chromosome in the nucleoid. Yet the term ‘nucleoid‐associated protein’, or NAP, is usually reserved for another group of DNA‐binding proteins, not all of which are sequence‐dependent for DNA binding. Most NAPs were discovered in roles other than organising the nucleoid. Several were first encountered as contributors to the efficient operation of site‐specific recombination systems in bacteria or their phage (reviewed in Dorman and Bogue 2016). Later, their more general contributions to cell physiology became appreciated. We have already encountered two, FIS and IHF, as components of the systems that govern the initiation of chromosome replication (Section 1.3). Originally, FIS was identified as an enhancer‐binding protein that improved the efficiency of the DNA inversion events responsible for phase‐variable expression of tail fibre genes in bacteriophage Mu, and for flagellar phase variation in Salmonella (Koch and Kahmann 1986; Johnson et al. 1986). IHF was detected as an essential factor for the site‐specific entry of the bacteriophage lambda genome into the attλ site on the chromosome of E. coli (Nash and Robertson 1981) (Section 1.35). These and other NAPs have emerged as important regulators of a multitude of bacterial genes (Dillon and Dorman 2010). They have mechanisms of action that typically involve the making of adjustments to local DNA architecture. In many cases, these adjustments affect gene expression at the level of transcription (or beyond) and include direct or indirect effects on nucleoid structure. A summary of the key features of some of the most important (i.e. best‐studied) NAPs is given in the following sections.