Mucorales encode a stand-alone RNA ligase enzyme active in tRNA splicing in vivo. (A) Alignment of the primary structures of monofunctional Trl1 LIG domain homologs from M. circinelloides (Genbank EPB83728.1), R. azygosporus (Genbank RCH90547.1), and L. corymbifera (Genbank CDH55495.1). Positions of side chain identity/similarity are indicated by dots. Six signature ligase adenylyltransferase motifs I, Ia, III, IIIa, IV, and V are shaded in cyan. Two conserved arginine residues implicated in the recognition of an RNA 2′-PO4 terminus are shaded in yellow. (B) Complementation of S. cerevisiae trl1Δ was assayed by plasmid shuffle. Aliquots (3 µL) of serial tenfold dilutions of FOA-resistant trl1Δ strains expressing the indicated genes were spotted on YPD agar plates and incubated at 25°C, 30°C, 34°C, and 37°C. Photographs of the plates are shown.
