sentence: A 709-bp upstream region containing a 15-bp overlap with the 5 ′ end of abrB ( abrB fragment A ) and a 729-bp downstream region containing a 21-bp overlap with the 3 ′ end of abrB ( abrB fragment B ) were amplified from B. thuringiensis HD73 genomic DNA with the abrB-a / abrB-b and abrB-c / abrB-d primer sets , respectively .