Complete Genomic Nucleotide Sequence of the Temperate Bacteriophage AaΦ23 of Actinobacillus actinomycetemcomitans

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Abstract
The entire double-stranded DNA genome of the Actinobacillus actinomycetemcomitans bacteriophage AaΦ23 was sequenced. Linear DNA contained in the phage particles is circularly permuted and terminally redundant. Therefore, the physical map of the phage genome is circular. Its size is 43,033 bp with an overall molar G+C content of 42.5 mol%. Sixty-six potential open reading frames (ORFs) were identified, including an ORF resulting from a translational frameshift. A putative function could be assigned to 23 of them. Twenty-three other ORFs share homologies only with hypothetical proteins present in several bacteria or bacteriophages, and 20 ORFs seem to be specific for phage AaΦ23. The organization of the phage genome and several genetic functions share extensive similarities to that of the lambdoid phages. However, AaΦ23 encodes a DNA adenine methylase, and the DNA packaging strategy is more closely related to the P22 system. The attachment sites of AaΦ23 ( attP ) and several A. actinomycetemcomitans hosts ( attB ) are 49 bp long.