hnRNP-U/SAF-A is encoded by two differentially polyadenylated mRNAs in human cells

Scaffold attachment factor A (SAF-A; Romig et al. (1992) EMBO J. 11, 3431-3440) is a human nuclear protein with high affinity for SAR DNA (scaffold attached region; Laemmli et al. (1992) Curr. Opin. Cell. Biol. 2, 275-285). We isolated and sequenced two classes of cDNA clones coding for SAF-A and found that their coding sequences are identical with the coding sequence of hnRNP-U (Kiledjian and Dreyfuss (1992) EMBO J. 11, 2655-2664). The two classes of cDNA clones differ, however, in the length of their 3' untranslated region and result from the use of two different polyadenylation signals. This is consistent with Northern blotting experiments which show that two mRNAs with a length of 3.9 kb and 3.1 kb, respectively, exist in human cells. Using selective cDNA fragments as probes we show that the shorter mRNA lacks 800 nucleotides of the untranslated 3' end.