Leuconostoc lactis beta-galactosidase is encoded by two overlapping genes

Area of Science:

• Molecular Biology
• Microbial Genetics
• Enzymology

Background:

• Lactose metabolism is crucial in lactic acid bacteria.
• Understanding beta-galactosidase gene structure and function is key to lactose utilization.
• Heterologous expression systems are valuable for studying microbial genes.

Purpose of the Study:

• To clone and characterize the beta-galactosidase gene from Leuconostoc lactis.
• To determine the genetic organization and functional requirements for beta-galactosidase expression in E. coli.
• To investigate the evolutionary origin of the L. lactis beta-galactosidase genes.

Main Methods:

• Cloning of a 16-kb BamHI fragment from L. lactis pNZ63 into E. coli.
• Deletion and complementation analysis to identify the coding region.
• Nucleotide sequencing, protein size determination, N-terminal sequencing, and sequence alignment.

Main Results:

• A 5.8-kb SalI-BamHI fragment contains two overlapping genes, lacL (1,878 bp) and lacM (963 bp).
• lacL expression is essential for LacM production, and both genes are required for functional beta-galactosidase in E. coli.
• Deduced protein sequences show homology to other beta-galactosidases, suggesting an internal deletion in an ancestral gene.

Conclusions:

• The L. lactis beta-galactosidase is encoded by two distinct genes, lacL and lacM.
• Both lacL and lacM are necessary for enzyme activity, with lacL regulating lacM expression.
• The L. lactis beta-galactosidase genes likely evolved from a single ancestral gene through internal deletion.