Variable aberrant cDNAs in single diphtheria toxin-resistant human fibroblasts

We treated transformed human fibroblasts with diphtheria toxin (DT) and isolated 40 single cells that were toxin resistant but unable to propagate. In 13 of them toxin resistance was associated with the presence of one or more aberrant transcripts of the structural gene for elongation factor 2 (EF-2). cDNA obtained from these transcripts had 164-447 bp-long deletions. Each of these deletions was associated with 2-8 base pairs-long repeats at its breakpoints. Only 10 out of 16 cDNA deletions were associated with presumed exon junctions. A role is suggested for errors in transcription in producing the aberrant transcripts which gave rise to the deletion-bearing cDNA species.