Amino‐Acid Sequence of lac Repressor from Escherichia coli

Abstract

The lac repressor from Escherichia coli, composed of four identical subunits with a molecular weight of 37 160, was carboxymethylated and fragmented by tryptic digestion and cyanogen bromide treatment. Using ion-exchange chromatography, gel filtration and preparative thin-layer electrophoresis and chromatography 29 of the 30 tryptic peptides were isolated in pure form. Direct Edman degradation and the dansyl-Edman technique were used to determine the sequence of the small tryptic peptides. Special emphasis was put on the sequence determination of the six large tryptic fragments which together account for 177 residues, corresponding to 51% of the repressor subunit with its 347 residues. The large tryptic fragments were analyzed after fragmentation with chymotrypsin, thermolysin and dipeptidyl aminopeptidase I. Thus the sequence of all 30 tryptic peptides could be deduced. The complete sequences of all cyanogen bromide fragments were deduced from peptides obtained by tryptic, chymotryptic and thermolytic digestion of the individual fragments and by automated stepwise Edman degradation of lac repressor and of the large cyanogen bromide fragments. The order of the cyanogen bromide fragments was given by overlapping tryptic peptides. The resulting amino acid composition of the monomer is Aspls, Asn,,, Thr18, Ser,,, GluI4, Gln2,, Prol3, Gly,,, Ala,, CYS,, Val,,, Met,, h7, Leu,,, Tyr,, Phe,, Trp,, Lys,,, His,, Arg,,.The sequence of lac repressor shows no similarities with that of other proteins known to bind to DNA or RNA. The N-terminal55 residues contain two homologous regions. This part of the sequence which is involved in lac operator binding might have been formed by gene duplication.The lactose ( l u c ) repressor of Escherichia coli controls the lac operon, which consists of three structural genes (z, y and a ) encoding fl-galactosidase, galactosidase permease, and thiogalactoside transacetylase, respectively. The lac operon also contains two controlling regions, the lac operator, which is the site of action for the repressor, and the lac promoter, which is the site of initiation of transcription by RNA ' Deceased March 13. 1972. This work is dedicated to his memory.Abbreviations. /ac, thc lactose operon ; dansyl or Dns l-dimethylaniinonaphtlialene-5-sulfonyl; CNBr, cyanogcn bromide; Quadrol, N , N , N ' , N'-tetrakis(2-hydroxypropyl)ethylenediamine; cyclic AMP, adenosine 3': 5'-monophosphate. Abbreviations for amino acids follow CBN rules, see Eur. J. Biochem. 27, 201 -207 (1972). In the presence of saturating amounts of inducer the repressor-operator complex decays and a repressorinducer complex is formed which has an approximately 1000-fold lower affinity for the operator compared to free repressor [7]. The elucidation of the molecular mechanism of the repressor-operator interaction requires knowledge of the structures of repressor and operator and of its complex. Accordingly, we embarked on the task of elucidating the amino-acid sequence of repressor. The sequence of lac operator has been reported recently b...

Purification and complete primary structures of the heparin-, cell-, and DNA-binding domains of bovine plasma fibronectin

“…They also report [38] similar sequences in ubiquitin, VKLTL [46], and in the Lac repressor protein, KPVTL [47]. These are both DNA-binding proteins.…”

Base-pair substitution hotspots in GAG and GCG nucleotide sequences in Escherichia coli K-12 induced by cis-diamminedichloroplatinum (II).

“…The base sequences are as reported by Farabaugh (32), except for 025, at which the sequence is in accordance with the amino acid sequence described by Beyreuther et al (33,34). To obtain the nonsense codons, the italic base pairs have to be replaced.…”

Biological Activity and a Partial Amino‐Acid Sequence of Escherichia coli DNA‐Binding Protein I Isolated from Overproducing Cells

“…The digestion was terminated by lyophilization after 12 h. The peptides were redissolved in 0.010 ml of 10 % acetic acid, centrifuged at 10000 x g for 10 min and 0.005 ml each were applied on two 20 x 20 cm cellulose thin-layer plates (0.1 mm cellulose, Schleicher & Schull, Dassel, FRG). The plates were developed by the fingerprint technique using electrophoretic separation at pH 6.5 or pH 2.1 and chromatography as described previously [21]. Peptides were eluted from the plates after staining with fluorescamine [16,21] and characterized by N-terminal and amino acid analyses.…”

“…The plates were developed by the fingerprint technique using electrophoretic separation at pH 6.5 or pH 2.1 and chromatography as described previously [21]. Peptides were eluted from the plates after staining with fluorescamine [16,21] and characterized by N-terminal and amino acid analyses.…”