Evolution in biosynthetic pathways: two enzymes catalyzing consecutive steps in methionine biosynthesis originate from a common ancestor and possess a similar regulatory region.

Abstract

The metC gene of Escherichia coli K-12 was cloned and the nucleotide sequence of the metC gene and its flanking regions was determined. The translation initiation codon was identified by sequencing the NH2-terminal part of 13-cystathionase, the MetC gene product. The meIC gene (1185 nucleotides) encodes a protein having 395 amino acid residues.The 5' noncoding region was found to contain a "Met box" homologous to sequences suggestive of operator structures upstream from other methionine genes that are controlled by the product of the pleiotropic regulatory metJ gene. The deduced amino acid sequence of (3-cystathionase showed extensive homology with that of the MetB protein (cystathionine y-synthase) that catalyzes the preceding step in methionine biosynthesis. The homology strongly suggests that the structural genes for the MetB and MetC proteins evolved from a common ancestral gene.

Design and implementation of three incoherent feed-forward motif based biological concentration sensors

“…This promoter is regulated by MetJ through the binding of ''met boxes'' to down-regulate transcription and is involved in methionine regulation (Weissbach and Brot 1991). The met operator in E. coli consists of tandem repeats of eight base pair sequences, homologous to a palindromic consensus AGACGTCT, known as ''met boxes'' (Belfaiza et al 1986). …”

“…With the introduction of the metJ gene on a pBR322 derivative under the control of T7-RNAP, GFP is produced from a T7-RNAP/metR hybrid promoter region (Fig. 6a) pair sequences, homologous to a palindromic consensus AGACGTCT, known as ''met boxes'' (Belfaiza et al 1986). There are 4 met boxes in the metR promoter of E. coli.…”

Cloning, purification, and crystallization of Escherichia coli cystathionine β‐lyase

“…The metC gene was cloned by PCR [12] from genomic DNA of E. coli K 12, using primers synthesized according to the published DNA sequence [1], but with an extra BamHI site at the 5'-ends (Primer 1: 5'-TAC TCA GGA TCC ATG GCG GAC AAA AAG CTT GAT ACT CAA CTG G-3'; Primer 2: 5'-GCG TGA GGA TCC TTA TAC AAT TCG CGC AAA ACC GGC-3'; BamHI-sites and start-codon underlined). The 1,1 kb DNA-fragment was isolated after BamHI treatment by preparative agarose gel electrophoresis and subsequently ligated into the BamHI-site of the tac-promoter vector pDR540.…”

“…The E. coli enzyme is composed of four identical subunits of 395 amino acids (MW 43,032) each [1], encoded by the metC gene. Each subunit contains one molecule of PLP as a cofactor, transiently bound at the active site through a Schiff base with lysine 210 [2].…”

“…CL has been shown to share extensive homology with cystathionine ~'-synthase, which catalyzes step two in methionine biosynthesis, i.e. formation of cystathionine from O-succinylhomoserine and cysteine, and a common evolutional origin of the two enzymes has been suggested [1,3].…”