φX174 lysis requires slyD , a host gene which is related to the FKBP family of peptidyl‐prolyl cis‐trans isomerases

Recessive mutations in the slyD (sensitivity to ly sis) gene were isolated by selecting for survival after induction of the cloned lysis gene E of bacteriophage φX174 [1]. The slyD − mutation, transduced into the normal φX174 host, Escherichia coli C, confers an absolute block on the plaque‐forming ability of the wild‐type phage, indicating that slyD is required for E function. slyD encodes a protein with 196 residues. A segment corresponding to the first 142 residues of the predicted SlyD protein has significant similarity throughout its length to the FKBP family of peptidyl‐prolyl cis‐trans isomerases, or rotamases. The C‐terminal 46 codons of slyD encode a remarkable histidine‐rich peptide which is a metal‐binding domain [2]. This sequence is dispensable for slyD function in E ‐mediated lysis. Although there is no obvious phenotype associated with the slyD − genotype other than the resistance to E ‐mediated lysis, overexpression of slyD causes cells to filament and to increase significantly in diameter. Mutations in φX174 can restore the plaque‐forming ability of the phage on a slyD − host. These pos ( p lates on s lyD) mutants plate on E. coli C wild‐type and slyD − . A model for SlyD involvement in E function and the role of SlyD in the cell is discussed.