THE 2-STEP LYSIS SYSTEM OF PNEUMOCOCCAL BACTERIOPHAGE-EJ-1 IS FUNCTIONAL IN GRAM-NEGATIVE BACTERIA - TRIGGERING OF THE MAJOR PNEUMOCOCCAL AUTOLYSIN IN ESCHERICHIA-COLI

The holin function Ejh of the pneumococcal bacteriophage EJ-1 has been characterized. It shows structural features similar to, and functiona lly complemented, the prototype member of the holin family. In Escheri chia coli and Pseudomonas putida the Ejh product caused cellular death , and changes in cell morphology could be accounted for by lesions in the cytoplasmic membrane, Expression of ejh resulted in the inhibition of growth in a variety of phylogenetically distant bacterial genera, suggesting a broad spectrum of action. Concomitant expression of the e jh and ejl (encodes a lysin) genes led to lysis of E. coli and P. puti da cells. Remarkably, the Ejl lysin was able to attack murein from bac teria lacking choline in their sacculi, which suggests that pneumococc al lysins have a broader substrate specificity than previously assumed . Furthermore, the Ejh holin was able to trigger activity of the major pneumococcal autolysin cloned and expressed in E. coil, and this rais ed new questions about the regulation of this model autolysin. A new f unction for holins in systems where the phage lysin is supposed to be associated with the membrane is proposed.