Summary: A 4·3 kb restriction fragment of DNA from G12 hybridized with a synthetic oligonucleotide representing the N-terminus of the sialidase protein secreted by This cloned fragment was shown to encode only part of the sialidase protein. The sialidase gene of C. was completed by a 0·7 kb restriction fragment overlapping one end of the I fragment. After combining the two fragments and transformation of , a clone that expressed sialidase was obtained. The nucleotide sequence of the sialidase gene of G12 was determined. The sequence of the 18 N-terminal amino acids of the purified extracellular enzyme perfectly matched the predicted amino acid sequence near the beginning of the structural gene. The amino acid sequence derived from the complete gene corresponds to a protein with a molecular mass of 44735 Da. Upstream from the putative ATG initiation codon, ribosomal-binding site and promoter-like consensus sequences were found. The encoded protein has a leader sequence of 27 amino acids. The enzyme expressed in has similar properties to the enzyme isolated from C. , except for small differences in size and isoelectric point. Significant homology (70%) was found with a sialidase gene from .


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