Nucleotide sequence and transcriptional analysis of activator-regulator proteins for beta-lactamase in Streptomyces cacaoi.

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RESUMO

The nucleotide sequence of the 2.7-kb DNA fragment upstream of the structural gene of beta-lactamase in Streptomyces cacaoi was determined. Computer-aided "FRAME" analysis revealed four possible open reading frames (ORFs), three in one direction and one in the opposite direction. One of them (ORF1, BlaA) encoded an activator-regulator protein whose deduced amino acid sequence was similar to that of other activator-regulator proteins in bacteria. Insertion of an 8-bp BamHI linker into the BlaA region decreased the beta-lactamase activity sharply, from 50 U to 1 U/ml. This protein (BlaA) was found to bind to the nucleotide sequence between the bla (beta-lactamase structural gene) and blaA genes. Another ORF (ORF2, BlaB) in the same orientation had a couple of amino acid sequences similar to that of pBR322 beta-lactamase. However, insertion of the 8-bp BamHI linker indicated that this ORF was functional as an activator-regulator but not as a beta-lactamase. Therefore, there were two activator-regulator proteins in the upstream region of the structural gene of the beta-lactamase. Nuclease S1 mapping predicted that transcription for the activator proteins commenced at the translational initiation codon or within a few nucleotides from the translational start site. Transcription was in the opposite direction to that of the beta-lactamase structural gene.

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