SSV1-ENCODED SITE-SPECIFIC RECOMBINATION SYSTEM IN SULFOLOBUS-SHIBATAE

We present evidence for the existence of a conservative site-specific recombination system in Archaea by demonstrating integrative recombination of Sulfolobus shibatae virus SSV1 DNA with the host chromosome, catalysed by the SSV1-encoded integrase in vitro. The putative int gene of SSV1 was expressed in Escherichia coli yielding a protein of about 39 kDa. This protein alone efficiently recombined linear DNA substrates containing chromosomal (attA) and viral (attP) attachment sites; recombination with either negatively or positively supercoiled SSV1 DNA was less efficient. Intermolecular attA x attA and attP x attP recombination was also promoted by the SSV integrase. The invariant 44 bp ''common attachment core'' present in all att sites contained sufficient information to allow recombination, whilst the flanking sequences effected the efficiency. These features clearly distinguish the SSV1 - encoded site - specific recombination system from others and make it suitable for the study of regulatory mechanisms of SSV1 genome - host chromosome interaction and investigations of the evolution of the recombination machinery.