CHARACTERIZATION OF A GENE ENCODING A MAJOR β-ENDOGLUCANASE FROM XANTHOMONAS ALBILINEANS

抄録

Initial reduction of the boundaries of the Xanthomonas albilineans (XAI-I) β-endoglucanase (egxA) gene encoded on a 7.1-kb DNA fragment resulted in the isolation of a 2.0-kb fragment encoding activity. Nucleotide sequence determination and analysis revealed an open reading frame (ORF) for the egxA gene starting at position 521bp, extending for 1, 086bp and coding for a 361-amino acid (aa) protein. Upstream of the egxA ORF, an additional ORF (ORF-2) and two Escherichia coli-like promoters (P₁ and P₂) were identified. The two promoter sequences were found to operate independently. Removal of P₁ and most of ORF-2 appeared to result in increased expression of egxA. Analysis of the deduced egxA as sequence revealed features common amongst known endoglucanases, including a proline-threonine-serine as region and a signal peptide with a predicted cleavage site after alanine²⁷. The protein displayed some degree of homology to members of the cellulase A family.