Beta-galactosidase

Some interesting facts [1]

• A tetramer of 4 identical subunits
• Each subunit is 120kD.
• Active only as a tetramer.
• Mutations in some of the codons of the N-terminal 60aa or C-terminal 100aa results in an inactive, dimeric β-galactosidase. [2]
• If the above sequences are deleted, the missing protein fragment can be replaced by the corresponding peptide. This is called intracistronic alpha or omega complementation respectively.
• Its N-terminal 23 residues can be replaced by any amino acid residues without affecting the enzymatic activity.
• A mutant with an internal deletion of codons 21-41 of the lacZ gene does not produce any active β-galactosidase.
• A mutant with a deletion of everything past residue 60 (i.e. it expresses only the first 60 N-terminal amino acids) does not produce any active β-galactosidase.
• You can measure lacZ activity using flow cytometry. See A flow cytometric study of stationary phase gene expression in E.coli using lacZ reporter gene fusion

Reference

1. ISBN:3-11-014830-7
2. ISBN:0317118099
3. Ullmann A. Complementation in beta-galactosidase: from protein structure to genetic engineering. Bioessays. 1992 Mar;14(3):201-5. DOI:10.1002/bies.950140311 |