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  • Title: Substitution of glutamine-60 with glutamic acid causes the lac permease of Escherichia coli to become temperature sensitive.
    Author: Sarkar HK, Viitanen PV, Poonian MS, Kaback HR.
    Journal: Biochemistry; 1986 May 20; 25(10):2778-81. PubMed ID: 2872916.
    Abstract:
    The lac Y gene of Escherichia coli was modified by oligonucleotide-directed, site-specific mutagenesis so that Gln-60 is replaced with Glu. Although the replacement introduces a negative charge into a putative hydrophobic, transmembrane alpha-helical segment of the lac permease, lactose/H+ symport is unimpaired. However, the modified permease is more susceptible to heat inactivation. That is, upon incubation at 45 degrees C, Glu-60 permease loses activity with a t1/2 of 20 min relative to a t1/2 of 50 min with wild-type permease.
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