Pilin Genes of Moraxella lacunata

as a hybridization probe to screen a A ZAP library ofM. lacunaa DNA, we have isolated a cone that not only contains the entire type 4 pUin gene inversion region of M. lacunata but inverts the 2-kb regin on a plsmid subclone (pMxLl) in Escherichia coli. Deletion derivatives of pMxLl yielded some plamds that stil had the entire inversion region but were phase locked into one or the other of the two potentia orwienato. Simlarly, insertions of a 2-kb streptomycin-resistant element (Qi) within some regions outside of the inversion also resulted in phase-locked plasmids. These deletions and insertions thus localize a probable invertase for the inversion event. The region was sequenced, and an open reading frame with over 98% DNA sequence homology to an open reading frame that we previously found in M. bovis and called ORF2 appeared to be a strong candidate for the invertase. This conclusion was confirmed when a plasmid contning the M. bovis ORF2 suppled, in trans, the inversion function missing from one of the M. lacunata phase-locked inversion mu,tants. We have named these putative invertase genes piv,, (pilin inversion of M. lacunata) and PiV,b (plin inversion ofM. bovis). Despite previously noted sequence as between theM. bovis sites of inversion and those of the Hin family of inverbkle segments and a 60-base-pair region within the inversion with 50% sequence similarit to the ciin recombinational enhancer, there is no significant sequence similarity of the Piv invertases to the Hin' family of invertases.