Biosynthetic alr alanine racemase from Salmonella typhimurium: DNA and protein sequence determination

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Alanine racemase is crucial for bacterial cell wall synthesis.
• Salmonella typhimurium possesses both biosynthetic (alr) and catabolic (dadB) alanine racemase genes.

Purpose of the Study:

• To determine the nucleotide sequence of the alr gene in Salmonella typhimurium.
• To compare the alr gene and its product with the dadB gene and its product.

Main Methods:

• Dideoxy chain termination sequencing (Sanger method).
• Shotgun cloning and specific subcloning.
• Use of synthetic site-specific primers for sequence assembly.

Main Results:

• The alr gene is 1077 base pairs long, encoding a 359-amino acid protein.
• The alr and dadB genes show high similarity in size (1077 vs. 1068 bp) and 52% sequence identity.
• The encoded proteins share 43% homology, including the pyridoxal 5'-phosphate binding site.

Conclusions:

• The nucleotide sequence of the Salmonella typhimurium alr gene has been elucidated.
• Significant sequence and homology exist between the biosynthetic (alr) and catabolic (dadB) alanine racemase genes and their products.