All the essential genetic determinants for site-specific integration of corynephage AAU2 are contained within a 1,756-bp DNA fragment, carried on the integrative plasmid p5510, and are shown to be functional in Escherichia coli. One open reading frame, ORF4, encoding a protein of 266 amino acids was shown to represent the AAU2 integrase. The nucleotide sequence of the AAU2 attachment site, attP, and the attB, attL, and attR sequences in the host ''Arthrobacter aureus'' C70 were determined. Identical nucleotide sequences were shown to be responsible for the integration of p5510 in the chromosomes of Corynebacterium glutamicum, Brevibacterium divaricatum, and B. lactofermentum, and a sequence almost identical to attB was found to be present in these three strains. In contrast to other phage site-specific recombination systems, a plasmid encompassing only int-attP failed to integrate into the host chromosome. This led to the identification of an 800-bp noncoding region, immediately upstream of int, absolutely required for site-specific integration of p5510.Genera Arthrobacter, Corynebacterium, and Brevibacterium belong to the group of coryneform bacteria from which several strains are industrially used for the production of certain amino acids (52). Most of the corynephages isolated to date originated from fermentation failures or soils and are virulent (19,45,47,51). AAU2 is a temperate phage isolated from soil that infects and lysogenizes ''Arthrobacter aureus '' C70 (24). Other known temperate corynephages have been isolated following UV or mitomycin induction of coryneform strains (20,29,30,34,42). Thus, a significant proportion of strains were shown to harbor prophages, but only for a few of them was the phage-host relationship studied (30, 42). The only well-documented temperate corynephage is phage  of the human pathogen Corynebacterium diphtheriae (18). Its integration occurred into either of two sites (attB1 and attB2) located on the C. diphtheriae chromosome (36). These attB sites share a 96-bp sequence with the attP sites of -related phages (37). Moreover, screening of a variety of Corynebacterium species including the soil isolate C. glutamicum ATCC 13032 with attP and attB probes showed that all of the species investigated contained at least one DNA fragment that hybridized with both of these probes (8,9,15). Besides this report, information on the molecular biology of lysogeny in coryneform bacteria remained scarce.The present study reports on the phage-encoded site-specific recombination system of AAU2, which has been pinpointed previously to a 5.25-kb BglII-EcoRV fragment on the phage genome (24). The phage attachment sites (attP, attB, attR, and attL) were sequenced, and a common sequence was identified. The AAU2 integrase gene was also delineated by transposon mutagenesis, and its deduced protein sequence was shown to resemble the conserved C-terminal region of other members of the integrase family. MATERIALS AND METHODSBacteriophage, bacterial strains, and plasmids. The bacteriophage, bacteria...
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