Escherichia coli B/r leuK mutant lacking pseudouridine synthase I activity

Area of Science:

• Molecular Biology
• Microbial Genetics

Background:

• Escherichia coli strain EB146 (leuK16) exhibits elevated enzyme levels for amino acid synthesis.
• This strain shares characteristics with E. coli and Salmonella typhimurium hisT strains.

Purpose of the Study:

• To investigate the molecular basis of the leuK16 mutation's effects.
• To determine the relationship between the leuK locus and pseudouridine synthesis.

Main Methods:

• Analysis of tRNA modifications in leuK and hisT strains.
• Assay of pseudouridine synthase I activity in cell extracts.
• Complementation studies using plasmids containing the E. coli K-12 hisT locus.

Main Results:

• tRNA1Leu from leuK and hisT strains showed uridine instead of pseudouridine at specific positions.
• tRNA3Leu and tRNA4Leu from leuK strains had unmodified uridine residues.
• Pseudouridine synthase I activity was absent in leuK16 extracts.
• Phenotypes of leuK16 were complemented by a plasmid carrying the hisT locus.

Conclusions:

• The leuK locus is likely identical to the hisT locus, encoding pseudouridine synthase I.
• Alternatively, leuK may encode a factor influencing pseudouridine synthase I activity.