Sequence of the short 3 0 UTR is highly similar in the rat and human genes (up to 90% of homology in the conserved region), but in the further region of the long 3 0 UTR similarity abruptly decreases, which is consistent with the observation that there is only one (short) Pol b transcript in the human cells. Sequence similarity indicates that regulatory motifs present in the short 3 0 UTR of the rat Pol b transcript may act in the same manner and bind similar factors in human cells.