Structures of the Euplotes crassusTec1 and Tec2 elements: identification of putative transposase coding regions

Abstract

The Tec 1 and Tec 2 transposon-like element families of Euplotes crassus are highly unusual in that all 30 000 copies of each family are excised from the genome during a discrete time period of macronuclear development. Complete nucleotide sequences were generated for the Tec 1-1 and Tec 2-1 elements, representing the Tec 7 and Tec 2 families. Open reading frames (ORFs) are conserved in position and sequence between the two elements, although sequences that comprise one ORF (ORF2) of Tec 1-1 are split into two overlapping ORFs (ORFs 2A and 2B) in Tec 2-1. ORF1 in Tec 1-1, its homolog in Tec 2-1 and one of the overlapping ORFs from Tec 2-1 (ORF2B) contain TGA codons, which may be translated as Cys, as observed for two other Euplotid genes. Sequence analyses of ORFs from other members of each element family indicate that the families are distinct from each other and are highly conserved within each family. Computer searches of sequence databases have revealed sequence similarity between Tec ORF 1s and the previously described Tc 1-IS 630 family of transposases which includes ORFs from bacterial, nematode and insect transposons.