Fig. 4.

GLD-2-related sequences and candidate PAPs. (A) polβ-nucleotidyl transferase family. The family includes not only GLD-2 (and the DNA polymerases, Trf4p and Trf5p, of Saccharomyces cerevisiae), but also CCA-adding enzymes (CCA), 2′-5′oligo(A) synthetases (2′-5′A), terminal transferase (TdT), the polX polymerases, and enzymes that transfer nucleotidyl groups to other nonnucleic acid compounds. The image is based on Aravind and Koonin (31). (B) Cladogram of a subset of sequences most similar to GLD-2, emphasizing those relevant for this work. Sequences tested for PAP activity are in boxes. Black boxes, proteins that possessed PAP activity as tethered proteins; white boxes with an “X,” proteins without activity as tethered proteins (although the proteins were expressed); gray boxes, sequences shown in other work to be cytoplasmic PAPs (27, 28). Hs2 and Hs4 proteins were expressed at too low levels to be assessed confidently. “bPAP” indicates the canonical nuclear PAP derived from Bos taurus: the other canonical PAPs are very closely related. (C) Structure of the GLD-2 relatives tested. Gray boxes, catalytic domains; black boxes, central domains; RRM, the RRM-like region present in canonical nuclear PAPs; white boxes, other regions. Hs2 also has a retrovirus zinc-finger-like domain.