Structure of gene and pseudogenes of human apoferritin H.

Ferritin is composed of two subunits, H and L. cDNA's coding for these proteins from human liver (1,2,3), lymphocytes (4) and from the monocyte-like cell line U937 (5) have been cloned and sequenced. Southern blot analysis on total human DNA reveals that there are many DNA segments hybridizing to the apoferritin H and L cDNA probes (1,2,4,6). In view of the tissue heterogeneity of ferritin molecules (7,8), it appeared possible that apoferritin molecules could be coded by a family of genes differentially expressed in various tissues (1,2). In this paper we describe the cloning and sequencing of the gene coding for human apoferritin H. This gene has three introns; the exon sequence is identical to that of cDNA's isolated from human liver, lymphocytes, HeLa cells and endothelial cells. In addition we show that at least 15 intronless pseudogenes exist, with features suggesting that they were originated by reverse transcription and insertion. On the basis of these results we conclude that only one gene is responsible for the synthesis of the majority of apoferritin H mRNA in various tissues examined, and that probably all the other DNA segments hybridizing with apoferritin cDNA are pseudogenes.