P{HBΔ-23} insertion in the first intron between nucleotides 3917 and 3919. Nucleotide 3918 of sesB is deleted and the insertion is associated with 47bp of unidentified sequence between the sesB sequence and the 3' end of the P{HBΔ-23} element and 58bp of unidentified sequence between sesB and the 5' end of the P{HBΔ-23} element.