Molecular characterization of an autolysin-defective mutant of Streptococcus pneumoniae

The mutant gene lyt-4 of the autolysin-defective mutant R6ly4-4 of Streptococcus pneumoniae, which synthesized a temperature-sensitive autolytic enzyme, has been cloned in Escherichia coli. The nucleotide defect of the lyt-4 mutation has been characterized as a CG to TA transition. This transition causes the appearance of a glutamic acid instead of a glycine in the amino acid sequence of the autolysin, altering the hydropathic profile of the protein. This alteration might explain the observed thermosensitivity of the mutated autolytic enzyme. The present work represents the first molecular characterization of a mutation in the structural gene of a bacterial autolysin.