FIGURE 4.

The correlation between the β-galactosidase allolactose synthesis motif and lac repressors in microbial genomes. The figure shows part of a larger tree of β-galactosidase sequences, restricted to the one branch of the tree where the allolactose synthesis motif was identified. A node label colored blue and preceded by a + symbol indicates a lac repressor was identified in the same genome. The node labels indicate genus, species, and β-galactosidase sequence accession number. Motif lists the residues that align with E. coli β-galactosidase allolactose synthesis motif in the order 517, 599, 808, 795, 796, 797, 798, 799, 800, 801, 802, 803, 804, and 805. Those residues that are conserved relative to the E. coli protein are capitalized. Identity indicates the total number of the 14 motif residues that are strictly conserved with E. coli β-galactosidase. The complete version of this tree is shown in supplemental Fig. 2A, but note in this figure the node labels are colored by different criteria.