Two of the most abundant induced transcripts correspond to activated retro-elements. A B2-class SINE element, the murine equivalent of repetitive sequence DNA similar to human Alu, was induced during the first seven hours, reaching signal levels comparable to the globins. A VL30 endogenous retrotransposon was almost 20-fold induced over the course of the experiment. The probe sequence is similar to VL30 elements previously characterized as erythropoietin responsive in other cell lines 1,2. While not as abundant, a number of transcripts corresponding to intracisternal A particles, endogenous retroviruses, were also activated. The activation of endogenous retroviruses has been associated with loss of cytosine methylation by DNA methyltransferase-1 (Dnmt) 3 ,a gene which is repressed immediately after GATA-1 activation. The role of these apparently parasitic transcripts in normal erythropoiesis is not clear, but retrotransposition of these elements into cytokine genes and subsequent factor-independent transformation has been observed 4-7.
Viral-like sequences detected in G1E cells 0, 3, 7, 14, 21 and 30 hours after activation of GATA-1. 99849_at is VL30 like sequences, with homology to the MuLV LTR. 93909_at and 97181_at are similar to intracisternal A particles. The Affymetrix control sequence AFFX_MUR_B2 represents SINE B2 elements.