Abstract
Escherichia coli can overcome the toxicity of environmental cyanate by hydrolysis of cyanate to ammonia and bicarbonate. This reaction is catalyzed by the enzyme cyanase, encoded by the cynS gene. The nucleotide sequence of cynS has been reported (Sung, Y.-c., Anderson, P. M., and Fuchs, J. A. (1987) J. Bacteriol. 169, 5224-5230). The nucleotide sequence of the complete cyn operon has now been determined. The cyn operon is approximately 2600 base pairs and includes cynT, cynS, and cynX, which encode cyanate permease, cyanase, and a protein of unknown function, respectively. Two cyanate-inducible transcripts of 1500 and 2500 nucleotides, respectively, were detected by Northern blot analysis. S1 nuclease mapping experiments indicated that two different cyn mRNAs have a common 5'-end and two different 3'-ends. One 3'-end was located within the coding region of cynX, whereas the other 3'-end includes the entire DNA sequence of cynX. The longer transcript contained 98 nucleotides complementary to lac mRNA produced by the predominant lac transcription termination sequence. Termination vectors were used to show that both 3'-ends were generated by sequences that caused transcriptional termination in vivo. Expression vectors were used to demonstrate that a protein corresponding to the expected size was synthesized from the DNA fragment containing the open reading frame designated cynX. The predicted amino acid sequence of cynX indicates that it is a very hydrophobic protein. The level of cynX expression was significantly less than that of cynT or cynS expression.
Highlights
Of the complete cyn operon has been determined
The operon is composed of three genes, includes cynT, cynS, and cynX, which encode cyanate cynT, cynS, and cynX, encoding cyanate permease, cyanase, permease, cyanase, and a protein of unknown function, and a protein of unknown function, respectively
The two 3’-ends were found to be experiments indicated that two different c y n mRNAs generated byDNA sequences capable of terminating tranhave a common 5’-end and two different 3’-ends.One scription
Summary
Of the complete cyn operon has been determined. In this paper, the nucleotide sequence of the entire cyn. Cyanate permease was found to have a M , of 26,000 as determined by sodium dodecyl sulfate-polyacrylamide (15%) gel electrophoresis [9].’ A potential Shine-Dalgarno sequence (GAGG) was found six nucleotides upstream from the translation initiation codon of cynT (Fig. 2).
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