SummaryThe nucleotide sequence of thevirGlocus of the nopaline type plasmid pTiC58 ofAgrobacterium tumefacienshas been determined. It contains an open reading frame (ORF) of 759 nucleotides and has 77% homology to thevirGsequences of octopine type plasmids. Differences between the sequences of the two types of Ti plasmids in the region ofvirGare located predominantly outside the ORF. The amino acid sequences inferred from the twovirGgenes show 80% homology to each other and each shows the same moderate homologies to amino acid sequences derived from genes in a family of two‐component regulatory systems. Specific differences in nucleotide and amino acid sequences as well as a structure‐function model for the gene product are discus