SummaryPhage I, like a number of other iarge DNA bacteriophages and the herpesviruses, produces concatemeric DNA during DNA replication. The concatemeric DNA is processed to produce unit-length, virion DNA by cutting at specific sites along the cortcatemer. DNA cutting is co-ordinated with DNA packaging, the process of translocation of the cut DNA into the preformed capsid precursor, the prohead. A key player in the X DNA packaging process is the phage-encoded enzyme terminase, which is involved in (i) recognition of (he concatemeric k DNA; (fi) initiation of packaging, which includes the introduction of staggered nicks at cosN to generate the cohesive ends of virion DNA and the binding of the proliead; (iii) DNA packaging, possibly including the ATP-driven DNA translocation; and (iv) following translocation, the cutting of the terminal cosN lo complete DNA packaging. To one side of cosN is the site cosB, which plays a role in the initiation of packaging; along with ATP, cosB stimulates the efficiency and adds fidelity to the endonuclease activity of terminase in cutting cosN. cosB is essential for the formation of a post-cleavage complex with terminase, complex I, that binds the prohead, forming a ternary assembly, complex II. Terminase interacts with cosN through its iarge subunit, gpA, and the small terminase subunit, gpNu1, interacts with cosB. Packaging follows complex 11 formation. cosN is flanked on the other side by the site cosQ, which is needed for termination, but not initiation, of DNA packaging. cosO is required for cutting of the second cosN, i.e. the cosW at which termination occurs. DNA packaging in X, has aspects that differ from other X DNA transactions. Unlike the site-specific Received

The formation of biofilms by Staphylococcus aureus and Staphylococcus epidermidis is an important aspect of many staphylococcal infections, most notably endocarditis, osteomyelitis and infections associated with indwelling medical devices. The major constituents of staphylococcal biofilms are polysaccharides, such as poly N-acetyl glucosamine (PIA/PNAG), cell surface and secreted bacterial proteins, and extracellular DNA. The exact composition of biofilms often varies considerably between different strains of staphylococci and between different sites of infection by the same strain. PIA/PNAG is synthesized by the products of four genes, icaADBC, that are encoded in a single operon. A fifth gene, icaR, is a negative regulator of icaADBC. Expression of icaADBC is tightly regulated, but can often be induced in vitro by growing staphylococci in the presence of high salt, high glucose, or ethanol. Regulation of icaADBC is complex and numerous regulatory factors have been implicated in control of icaADBC. Many of these are well known global transcriptional regulatory factors like SarA and sigmaB, whereas other regulators, such as IcaR, seem to affect expression of relatively few genes. Here, we will summarize how various regulatory factors affect the production of PIA/PNAG in staphylococci.

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