Bacillus cereus 569/H beta-lactamase I: cloning in Escherichia coli and signal sequence determination

The gene, penPC, for beta-lactamase I of Bacillus cereus 569/H has been cloned and its expression studied in Escherichia coli. The protein product from the in vitro translation of penPC was shown by gel electrophoresis to have an Mr of 36 000 which is larger than the in vivo products found in B. cereus and E. coli. The DNA sequence of the signal region was determined. It revealed that the smallest known mature form present in B. cereus culture fluids is preceded by 45-48 amino acids in pre-beta-lactamase I, considering that there are 3 initiation codons in the same reading frame, one or more of which might be initiating translation. Unlike the Bacillus licheniformis 749/C beta-lactamase, which has a membrane-bound thioether lipoprotein form, the single Cys residue in the B. cereus beta-lactamase I signal sequence is unmodified and a single processed form of the enzyme is present in E. coli cells carrying penPC.