FIG. 3.

Relationship among bacterial urocanases. Similarities between the enzymes have been shown as an unrooted neighbor-joining tree, giving all branch lengths (indicated by numerical values). The tree has been drawn by a neighbor-joining plot of the CLUSTAL X (version 1.8) program. The urocanase sequences of gram-negative bacteria (e.g., P. syringae, P. putida, P. aeruginosa, V. cholerae, and A. rhizogenes) and gram-positive bacteria (e.g., B. subtilis, S. coelicolor, and D. radiodurans) fall into two distinct clusters and may have diverged early in evolution. The only sequence of possible plant origin (33), from T. repens, is closer to the sequence of gram-negative bacteria.