IS1294, a DNA element that transposes by RC transposition

IS1294 found on the ColD-like resistance plasmid pUB2380, is IS91-like. It is an active 1.7-kb insertion sequence that lacks terminal inverted repents , displays insertion-site specificity, and dues not generate direct repeats of the target site. The clement has one large open reading frame. tnp(1294 ), encoding a transposase of 351 amino acids, related to members of the REP family of replication proteins used by RC-plasmids of gram-positive bacter ia. IS1294 transposes using rolling-circle replication, initiated at one en d of the element, oriIS, and terminated at the other, re, IS. oriIS and ter IS are highly conserved among like IS elements. oriIS resembles the leading strand replication origins of RC-plasmids; terIS resembles a rho-independe nt transcription terminator. IS1294 mediates not only its own transposition , but also sequences adjacent to terIS. A transposition model for IS1294 an d related elements, involving rolling-circle replication and single-strand DNA intermediates, is presented, (C) 2000 Academic Press.