TRANSCRIPTION OF TI PLASMID-DERIVED SEQUENCES IN 3 OCTOPINE-TYPE CROWN GALL TUMOR LINES

Total RNA isolated from 3 octopine-type crown gall lines contains sequences homologous to specific regions of the tumor-inducing (Ti) plasmid of Agrobacterium tumefaciens strain 15955. A comparison of transcripts in these 3 tumor lines suggests that tumor cells transcribe various sequences within a sector of plasmid DNA of 13 x 10 6 daltons and that transcription may not be uniform across the plasmid-derived sequences (T-DNA). Transcription of T-DNA by octopine-type tumors occurs at 4 major sites. The levels of transcription occurring at 3 of these sites appear to vary considerably among the 3 tumor lines investigated. Part of this variability may reflect differences in the organization and copy number of T-DNA. One of the transcription sites maps within a region of DNA with common sequence homology with all Ti plasmids. Varying amounts of transcript homologous to this region of T-DNA are present in all 3 tumor lines. It is suggested that transcription of these conserved sequences in the plant may have significance regarding the mechanism of tumorigenesis.