DNA coding for protein which confers on bacterium escherichia coli resistance to L-homoserine, and method for producing L-amino acids

Abstract

A bacterium which has an ability to produce an amino acid and in which a novel gene (rhtB) coding for a protein having an activity of making a bacterium having the protein L-homoserine-resistant is enhanced, is cultivated in a culture medium to produce and accumulate the amino acid in the medium, and the amino acid is recovered from the medium.

What is claimed is:  
     
         1 . A DNA coding for a protein as defined in the following (A) or (B): 
 (A) a protein which comprises an amino acid sequence shown in SEQ ID NO:2 in Sequence Listing; or    (B) a protein which comprises an amino acid sequence including deletion, substitution, insertion or addition of one or several amino acids in the amino acid sequence shown in SEQ ID NO:2 in Sequence Listing, and which has an activity of making a bacterium having the protein L-homoserine-resistant.    
     
     
         2 . The DNA according to  claim 1 , which is a DNA as defined in the following (a) or (b): 
 (a) a DNA which comprises a nucleotide sequence of the nucleotide numbers of 557 to 1171 of a nucleotide sequence shown in SEQ ID NO:1 in Sequence Listing; or    (b) a DNA which hybridizes with the nucleotide sequence of the nucleotide numbers of 557 to 1171 of the nucleotide sequence shown in SEQ ID NO:1 in Sequence Listing under stringent conditions, and which codes for the protein having the activity of making the bacterium having the protein L-homoserine-resistant.    
     
     
         3 . A bacterium belonging to the genus Escherichia, wherein L-homoserine resistance of said bacterium is enhanced by amplifying a copy number of the DNA as defined in  claim 1  in a cell of said bacterium.  
     
     
         4 . The bacterium according to  claim 3 , wherein the DNA as defined in  claim 1  is carried on a multicopy vector in the cell of said bacterium.  
     
     
         5 . The bacterium according to  claim 3 , wherein the DNA as defined in  claim 1  is carried on a transposon in the cell of said bacterium.  
     
     
         6 . A method for producing an amino acid, comprising the steps of: 
 cultivating the bacterium as defined in any one of  claims 3  to  5 , which has an ability to produce the amino acid, in a culture medium, to produce and accumulate the amino acid in the medium, and    recovering the amino acid from the medium.    
     
     
         7 . The method according to the  claim 6 , wherein said amino acid is at least one selected from the group consisting of L-homoserine, L-alanine, L-isoleucine, L-valine and L-threonine.