MOLECULAR ANALYSIS OF METHANOBACTERIUM PHAGE PSI-M2

The methanogenic archaeon Methanobacterium thermoautotrophicum Marburg is infected by the double-stranded DNA phage Psi M2. The complete pha ge genome sequence of 26 111 bp was established. Thirty-one open readi ng frames (orfs), all of them organized in the same direction of trans cription, were identified. On the basis of comparison of the deduced a mino acid sequences to known proteins and by searching for conserved m otifs, putative functions were assigned to the products of six orfs. T hese included three proteins involved in packaging DNA into the capsid , two putative phage structural proteins and a protein related to the Int family of site-specific recombinases. Analysis of the N-terminal a mino acid sequences of three phage-encoded proteins led to the identif ication of two genes encoding structural proteins and of peiP, the str uctural gene of pseudomurein endoisopeptidase. This enzyme is involved in the lysis of host cells, and it appears to belong to a novel enzym e family. peiP was overexpressed in Escherichia coli, and its product was shown to catalyse the in vitro lysis of M. thermoautotrophicum cel ls. Comparison of the phage Psi M2 DNA sequence with parts of the sequ ence of the wild-type phage Psi M1 suggests that Psi M2 is a deletion derivative, which formed by homologous recombination between two copie s of a direct repeat.