Structure and expression of genes coding for xylan-degrading enzymes of Bacillus pumilus

The complete nucleotide sequence of the β-xylosidase gene (xynB) of Bacillus pumilus IPO and its flanking regions was established. A 1617-bp open reading frame for β-xylosidase, a homodimer enzyme, was observed. The amino acid sequence of the N-terminal region and the molecular mass (62607 Da) of the β-xylosidase subunit, deduced from the DNA sequence, agreed with the result obtained with the purified enzyme. The Shine-Dalgarno sequence was found 8 bp upstream of the initiation codon, ATG.

The xylanase gene (xynA) of the same strain was 4.6 kbp downstream of the 3′ end of xynB, and its DNA sequence was reported in our previous paper [Fukusaki, E., Panbangred, W., Shinmyo, A. & Okada, H. (1984) FEBS Lett. 171, 197–201]. The results of the Northérn hybridization suggested that the mRNA of xynA and xynB were produced separately. The 5′ and 3′ ends of the xynA and xynB gene were mapped with nuclease S1. The'-10′ regions for promoter sequences of both genes were similar to the consensus sequence for B. subtilis RNA polymerases, the'-35′ regions were different from all the known promoters for B. subtilis RNA polymerases.