PMID:4887874

Citation	Grodzicker, T and Zipser, D (1968) A mutation which creates a new site for the re-initiation of polypeptide synthesis in the z gene of the lac operon of Escherichia coli.J. Mol. Biol. 38:305-14
Abstract	No abstract in PubMed
Links	PubMed
Keywords	Polar Effect; Acyltransferases; Chromosome Mapping; Escherichia coli; Genes; Membrane Transport Proteins; Mutation; Operon; Translation; Suppressor
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Main Points of the Paper

• Polar effects of a UAG mutation in the operator-proximal region of the z gene are studied which leads to the isolation of two suppressor mutations
• π, a new site of initiation of protein synthesis is described
  • operates efficiently to restore permease and acetylase activity to a high level when induced
  • regulation/induction is still required, so the authors deduce that π is a new site of translation initiation (
  • not a new site of transcriptional initiation because acetylase is not present in the absence of inducer

Materials and Methods Used

• Parent Strain: NG545 (trp-8, Sm^S Hfr)
  • UAG mutation had not been altered in the suppressor strains isolated
• Strain: CA77B (Δlac, trp-8, Sm^R F^-)
• Strain: X103B (Δlac pro, trp-8, Sm^R F^-)
• Strain: M107 (Δlac, su_I⁺, Sm^R F^-)
• Strain: ΔLac_W (Δlac, his_-, Sm^R F^-)
• Strain: E29 (lac⁺ , F'/lac⁺, threonine^-, leucine^-, B₁^-, Sm^R)

• Acetylase assay
• β-galactosidase assay

Phenotype Annotations

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Species	Taxon ID	Strain	Gene (if known)	OMP	Phenotype	Details	Evidence	Notes
Escherichia coli	NCBI:562	NG545-pi(1)a	lacZ	Growth on melibiose medium Melibiose catabolic process	Growth	growth on melibiose- polar effects	Plating Assay	Table 2
Escherichia coli	NCBI:562	NG545-pi(1)	lacZ	Suppressor-dependent growth on lactose medium Suppressor-dependent lactose catabolic process	Growth	able to metabolize lactose only in a suI+ background	Plating Assay	Table 2- UAG polar mutation
Escherichia coli	NCBI:562	NG545-pi(1)b	lacZ	Abolished melibiose catabolic process Absent growth on melibiose medium	Growth	unable to metabolize melibiose/ growth on melibiose-polar effects	Plating Assay	Table 2-
Escherichia coli	NCBI:562	NG545-pi(1)a	lacZ	Decreased gene expression of beta-galactosidase Decreased lactose catabolic process	Metabolic Activity	trace amounts when induced	Biochemical Assay	Table 2
Escherichia coli	NCBI:562	NG545-pi(1)b	lacZ	reduced beta-galactosidase activity	Metabolic Activity	trace amounts when induced	Biochemical Assay	Table 2
Escherichia coli	NCBI:562	NG545B	lacZ	Decreased acetylase activity Decreased lactose catabolic process	Metabolic Activity	4.2% of the wild type level when induced	Biochemical Assay	Tables 3 and 4
Escherichia coli	NCBI:562	NG545	lacZ	Suppressor-dependent growth on lactose medium Suppressor-dependent lactose catabolic process	Growth	able to metabolize lactose only in a suI+ background	Plating Assay	Table 2- UAG polar mutation
Escherichia coli	NCBI:562	NG545-pi(1)	lacZ	Decreased acetylase activity Decreased lactose catabolic process	Metabolic Activity	35% of the wild type level when induced	Biochemical Assay	Tables 3 and 4
Escherichia coli	NCBI:562	NG24	lacZ	Decreased acetylase activity Decreased lactose catabolic process	Metabolic Activity	4.7% of the wild type level when induced	Biochemical Assay	Table 4
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References

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