We have sequenced a DNA fragment containing the Escherichia coli thrA-thrB junction, the complete thrB gene and the thrB-thrC junction. The intergenic sequence thrA and thrB is only one base pair. The coding region for homoserine kinase is 927 base pairs long. It is followed by 114 base pair segment in an open reading frame predicting that thrC begins just after non-sense codon of thrB. The presence at the end of thrA and of thrB of sequences that can pair with the 3' end of the 16 S ribosomal RNA suggests that reinitiation of translation occurs at the end of the two genes. The deduced aminoacid sequence for homoserine kinase shows no striking homology with aspartokinase I homoserine dehydrogenase I.