The conserved part of the T-region in Ti-plasmids expresses four proteins in bacteria.

The T-region of Ti-plasmids expresses four proteins (mol. wts. 74,000, 49,000, 28,000 and 27,000) in Escherichia coli minicells. Promoter activities are determined by sequences within the T-region, and the protein-coding regions map in that part of the T-region which is highly conserved in octopine and nopaline plasmids and which is responsible for shoot and root inhibition when expressed in plant cells. Three of the regions expressed in bacteria correlate with three regions which are transcribed in transformed plant cells; the fourth protein-coding region has no corresponding transcript in plants. At least three of the proteins synthesized in E. coli minicells are also expressed in cell-free systems prepared from E. coli and from Agrobacterium tumefaciens; the fourth protein (mol. wt. 49,000) is poorly expressed in both cell-free extracts. The possibility is discussed that the same genes are expressed in Agrobacteria and in transformed plant cells and that in both cases the gene products mediate growth regulatory effects to non-transformed plant cells.