This report describes the cloning and characterization
of a pseudouridine (Ψ) synthase from mouse that we
have named mouse pseudouridine
synthase 1 (mpus1p). The cDNA is ∼1.5
kb and when used as a probe on a Northern blot of mouse
RNA from tissues and cultured cells, several bands were
detected. The open reading frame is 393 amino acids and
has 35% identity over its length with yeast Ψ synthase
1 (pus1p). The recombinant protein was expressed in Escherichia
coli and the purified protein converted specific uridines
to Ψ in a number of tRNA substrates. The positions
modified in stoichiometric amounts in vitro were 27/28
in the anticodon stem and also positions 34 and 36 in the
anticodon of an intron containing tRNA. A human cDNA was
also cloned and the smaller open reading frame (348 amino
acids) was 92% identical over its length with mpus1p but
is shorter by 45 amino acids at the amino terminus. The
expressed recombinant human protein has no activity on
any of the tRNA substrates, most probably the result of
the truncated open reading frame.