Identification of a conditionally essential heat shock protein in Escherichia coli

Protein D48.5 was recognized as a heat-inducible protein of Escherichia coli during the screening of a group of random, temperature-inducible Mud-Lac fusion mutants. Physiological and genetic analysis demonstrated that (i) the structural gene for this protein, designated htpI, is a member of the o-32-dependent heat shock regulon, (ii) at 37°C the synthesis of protein D48.5 is nearly constitutive, increasing slightly with growth rate in media of different composition, and (iii) this protein is essential for growth at high temperature.