subsp. was shown to express extracellular xylanases. Genes encoding these enzymes were isolated from a gene library of subsp. DNA, constructed in bacteriophage λ47.1. One of the phages (PXC) that expressed xylanase also conferred the ability to hydrolyse carboxymethylcellulose. An 11.8 kb dIII DNA restriction fragment and a 6.2 kb RI DNA fragment were subcloned from two distinct xylanase-expressing phages, into pUC18, to yield recombinant plasmids pGHJ4 and pGHJ5 respectively. Cells of harbouring either of these two plasmids, or plasmid pJHH1 (comprising the cellulase gene from PXC, previously cloned on a 7.3 kb partial RI DNA fragment in pUC18), expressed xylanase activity. The positions of the xylanase genes in the recombinant plasmids were elucidated by subcloning and transposon mutagenesis. In pJHH1 the xylanase gene was adjacent to the DNA region encoding the endoglucanase. The polysaccharide-degrading genes in pJHH1 were transcribed from different promotors. Hybridization studies revealed that the xylanase genes encoded by pGHJ4 and pGHJ5 showed strong homology. All three cloned enzymes cleaved -nitrophenyl β--glucopyranoside and 4-methylumbelliferyl β--cellobioside. Xylan and glucose did not affect expression of xylanase in strains harbouring pJHH1, pGHJ4 or pGHJ5.


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