Messages encoding replication-dependent historic genes generally terminate with a stein-loop structure and lack polyadenylate tails. Adenylated historic transcripts were identified in Xenopus oocytes, though the role of the adenylate tracts is unknown. We report isolation of cDNAs from Xenopus embryos encoding historic mRNAs with 3' adenylate tracts. They also contain targets for stem-loop binding protein and U7 snRNA, which are required for histone RNA processing. One sequence is a read-through transcript containing a complete version of the downstream gene from the anti-parallel strand, similar to the RNAs from lampbrush loops of Notophthalmus oocytes. We injected read-through transcripts into Xenopus oocyte nuclei and they were processed to mature histone RNAs. Our results suggest that addition of 3' adenylate sequences might be a normal part of historic RNA synthesis. Also, these results shed light on the enigma of the developmental regulation of adenylated histone transcripts in Xenopus oocytes. (C) 2003 Elsevier Science (USA). All rights reserved.