A cryptic proline permease in Salmonella typhimurium

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Salmonella typhimurium utilizes three proline transport systems: PutP (high affinity), ProP, and ProU (lower affinity for proline, primarily for glycine betaine).
• The PutP system is essential for proline utilization as a sole carbon or nitrogen source.
• ProP and ProU are insufficient for proline utilization as a sole nutrient source.

Purpose of the Study:

• To clone and characterize a suppressor gene (proY) that enables proline utilization in a putP mutant.
• To investigate the mechanism by which proY facilitates proline utilization.

Main Methods:

• Genetic mapping of the proY gene on the S. typhimurium linkage map.
• DNA sequencing of the proY gene.
• Analysis of proY suppressor phenotype under different genetic conditions (multicopy plasmid, proZ mutation).

Main Results:

• The proY gene was mapped to 8 minutes on the S. typhimurium linkage map, distinct from known proline transport genes.
• DNA sequence analysis predicted proY encodes a hydrophobic integral membrane protein with homology to amino acid transporters.
• Proline utilization in a putP background required either multicopy proY or a single copy of proY combined with a proZ mutation.

Conclusions:

• The proY gene encodes a cryptic proline transporter.
• This transporter is typically inactive but can be activated by overexpression or a proZ mutation.
• Identifies a novel proline transport system in Salmonella typhimurium.