Beta-galactosidase

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Revision as of 13:05, 26 July 2007

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.

Reference

1. Benno Muller-Hill. The Lac Operon. Walter de Gruyter. isbn:3-11-014830-7. [Muller-Hill-1996]
2. isbn:0317118099. [Beckwith-1970]
3. Ullmann A. . pmid:1345751. PubMed HubMed [Ullmann-Bioessays-1992]