J. Biol. Chem., Vol. 261, Issue 24, 11156-11165, 08, 1986
Cloning and structure of the Bacillus subtilis aspartate transcarbamylase gene (pyrB)
CG Lerner and RL Switzer
The Bacillus subtilis gene (pyrB), which encodes aspartate transcarbamylase
(ATCase), was cloned on a HindIII restriction endonuclease fragment
inserted into the pUC13 plasmid vector. B. subtilis pyrB was expressed in
Escherichia coli, as judged by complementation of E. coli pyrB mutants and
production of enzyme that was specifically inhibited by antibody directed
against B. subtilis ATCase. The extent of expression was strongly dependent
on the orientation of the inserted DNA in the vector, which suggested that
transcription was initiated from vector-borne (rather than B. subtilis)
promoters. The entire 1098-base pair HindIII fragment of B. subtilis DNA
was sequenced by the Maxam-Gilbert method. The amino acid sequence of B.
subtilis ATCase was deduced from a 305-codon open reading frame and agreed
very well with analyses of the purified enzyme. Comparison of the sequence
of B. subtilis ATCase with that of E. coli ATCase catalytic subunit, for
which the three-dimensional structure is known, revealed many homologous
residues of probable importance in catalysis and structural folding of
ATCases. The significance of homology to E. coli ornithine
transcarbamylases was also analyzed. The sequences of the 5' and 3'
flanking regions to pyrB encode open reading frames in both cases which
overlap with pyrB by eight and six codons, respectively. It is probable
that these open reading frames encode other enzymes of a coordinately
regulated unit. The sequence 5' to pyrB also encodes an mRNA bearing a
pyrimidine-rich sequence followed by a typical sequence for a
rho-independent transcription terminator. The presence of these elements
and the 5' open reading frame suggest that B. subtilis pyrB, like E. coli
pyrBI, is regulated by an attenuation mechanism.