The Tec1 and Tec2 transposons of the ciliate Euplotes crassus carry a gene for a @entity669 -type site-specific recombinase. The expression of the Tec2 gene apparently uses a programmed +1 frameshift. To test this hypothesis, we first examined whether this gene has evolved under purifying selection in Tec1 and Tec2. Each element carries three genes, and each has evolved under purifying selection for the function of its encoded protein, as evidenced by a dearth of nonsynonymous changes. This distortion of divergence is apparent in codons both 5' and 3' of the frameshift site. Thus, Tec2 transposons have diverged from each other while using a programmed +1 frameshift to produce recombinase, the function of which is under purifying selection. What might this function be? @entity669 -type site-specific recombinases are extremely rare in eukaryotes, and @entity10093 elements are the first known eukaryotic type II transposons to encode a site-specific recombinase. @entity10093 elements also encode a widespread transposase. The @entity10093 recombinase might function in transposition, resolve products of transposition (bacterial replicative transposons use recombinase or resolvase to separate joined replicons), or provide a function that benefits the ciliate host. Transposons in ciliated protozoa are removed from the macronucleus, and it has been proposed that the transposons provide this "excisase" activity.

Selection on the genes of Euplotes crassus Tec1 and Tec2 transposons: evolutionary appearance of a programmed frameshift in a Tec2 gene encoding a XXXX family site-specific recombinase.

@entity669 :: ('CHEBI:18186', 'Chemical') :: ['tyrosine', 'Tyrosine'] @entity10093 :: ('7006', 'Gene') :: ['Tec']
@entity669 :: (CHEBI:18186,Chemical) :: ['tyrosine']
