Search for antisense copies of beta-globin mRNA in anemic mouse spleen

We reexamined critical aspects of the previous globin studies. We used intraperitoneal injections of phenylhydrazine to induce anemia in mice, as demonstrated by the appearance and ultimate disappearance of splenomegaly. While a 30-fold increase in globin mRNA was detected in the spleen, the relative amount of putative AS RNA could be no more than 0.004%.Contrary to earlier reports, induction of a major increase in globin transcripts in the mouse spleen was not associated with a detectable level of antisense RNA to globin mRNA.Over the years there have been numerous claims for the detection within prokaryotic and eukaryotic cells of antisense RNA sequences (AS). As recently reviewed by Kumar and Carmichael [1], many of the claims have been substantiated and in a subset of these, biological significance has been established. The origin of most of these AS sequences is transcription via DNA-directed RNA polymerization.A much more controversial issue is whether there is AS RNA that arises via RNA-directed RNA polymerization. Of course, for RNA viruses that encode their own polymerase activity, such AS RNA arises as a natural part of the replication cycle for the viral genome. And yet for the subviral RNA agents of plants known as viroids, and for the human (subviral) agent known as hepatitis delta virus (HDV), the replication of the RNA genome involves a host RNA polymerase [2]. Evidence has accumulated but not established that the relevant polymerase activity is via redirection of a polymerase that normally uses host DNA as a template. For example, it is considered that HDV replication and that of some plant viroids might involve redirection of the host RNA polymerase II [3, 4]. Other plant viroids are considered to replicate via redirection of a chloroplast polymerase activity [5].In contrast to such proposed redirection, studies in plants have found a non-viral host RNA-directed RNA polymerase activity [6,7,8]. After the gene for one of these was cloned and sequence