Analysis and DNA sequence of the osmoregulatedtreA gene encoding the periplasmic trehalase ofEscherichia coli K12

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Abstract
ThetreA gene ofEscherichia coli K12 codes for a periplasmic trehalase that is induced by growth at high osmolarity. The position oftreA within a cloned chromosomal DNA fragment was identified by subcloning of restriction fragments and analysis of the gene product in minicells. The nucleotide sequence of thetreA coding region as well as its upstream control region was determined. ThetreA gene consists of 1695 bp encoding 565 amino acids. The amino-terminus of the mature trehalase was found to begin with the amino acid Glu at position 31 of the open reading frame. The first 30 amino acids resemble a typical signal sequence, consistent with trehalase being a secreted periplasmic enzyme. Two previously isolatedphoA fusions to theosmA gene were transferred by homologous recombination on to atreA-containing plasmid and found to be withintreA. Analysis of the hybrid genes and their gene products aided the localization oftreA and the determination of its direction of transcription within the cloned chromosomal segment. ThetreA-phoA fusions encoded hybrid proteins which could be found in the periplasm. We found that at high osmolarity the normal pathway for the uptake and utilization of trehalose is blocked. Therefore, the function of the periplasmic trehalase is to provide the cell with the ability to utilize trehalose at high osmolarity by splitting it into glucose molecules that can subsequently be taken up by the phosphotransferase-mediated uptake system.