In the A20/2J BALB/c B cell lymphoma, Southern analysis revealed an insertion of approximately 6 kilobases of DNA into the first intron of one Ebd-allele. Two observations suggest that the rearrangement did not occur recently in the A20/2J subline. Firstly, normal and altered Ebd-alleles are present in equal numbers, and secondly, the LB 27.4 and LS 102.9 somatic cell hybrids formed at an earlier date both possess the rearrangement. Sequences of two cDNA clones, λEb-7 and λEb-125, selected from an A20/2J cDNA library prepared from poly [A+] RNA indicate that the rearranged Ebd-allele directs the synthesis of atypical Eb transcripts. The clones contain Eb sequence linked to a portion of retroviral-like intracisternal A-particle (IAP) genomic sequence, and they appear to be copies of mRNA produced by splicing between a 5′ donor site in the retroviral transcript and the 3′ acceptor site of the Eb gene's first intron. The longer λEb-125 insert corresponds to RNA that initiated in the 5′-untranslated region of the Eb gene. The 3′-end of the first Eb exon joins to long terminal repeat sequence, and retroviral sequence extends up to the splice junction with the second Eb exon; 3′ of the junction, the λEb-125 sequence corresponds to that of a correctly spliced Eb transcript. It seems feasible that the cDNA clones represent hybrid RNA synthesized by read-through transcription of the Eb coding region and an IAP element inserted into the first intron of the rearranged Ebd-allele.
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